Out of curiosity, what do you see with this for your banner-message-text:

banner-message-text='You are accessing a U.S. Government (USG) 
Information System (IS) that is provided for USG-authorized use only. By 
using this IS (which includes any device attached to this IS), you 
consent to the following conditions:\n -The USG routinely intercepts and 
monitors communications on this IS for purposes including, but not 
limited to, penetration testing, COMSEC monitoring, network operations 
and defense, personnel misconduct (PM), law enforcement (LE), and 
counterintelligence (CI) investigations.\n -At any time, the USG may 
inspect and seize data stored on this IS.\n -Communications using, or 
data stored on, this IS are not private, are subject to routine 
monitoring, interception, and search, and may be disclosed or used for 
any USG-authorized purpose.\n -This IS includes security measures (e.g., 
authentication and access controls) to protect USG interests -- not for 
your personal benefit or privacy.\n -Notwithstanding the above, using 
this IS does not constitute consent to PM, LE or CI investigative 
searching or monitoring of the content of privileged communications, or 
work product, related to personal representation or services by 
attorneys, psychotherapists, or clergy, and their assistants. Such 
communications and work product are private and confidential. See User 
Agreement for details.\nThis is a Federal computer (and/or it is 
directly connected to a Fermilab local network system) that is the 
property of the United States Government.  It is for authorized use 
only.  Users (authorized or unauthorized) have no explicit or implicit  
expectation of privacy.\nAny or all uses of this system and all files on 
this system may be intercepted, monitored, recorded, copied, audited, 
inspected, and disclosed to authorized site, Department of Energy and 
law enforcement personnel, as well as authorized officials of other 
agencies, both domestic and foreign. By using this system, the user 
consents to such interception, monitoring, recording, copying, auditing, 
inspection, and disclosure at the discretion of authorized site or 
Department of Energy personnel.\nUnauthorized or improper use of this 
system may result in administrative disciplinary action and civil and 
criminal penalties.  By continuing to use this system you indicate your 
awareness of and consent to these terms and conditions of use.\nLOG OFF 
IMMEDIATELY if you do not agree to the conditions stated in this 
warning.\nFermilab policy and rules for computing, including appropriate 
use, may be found at\nhttp://www.fnal.gov/cd/main/cpolicy.html\n'


I get a well formatted message on the side of the box similar to your 
"Medium Screen"

Pat

On 10/14/2015 02:47 PM, Sean wrote:
> I'll just paste the relevant stuff here:
>
>     # banner stuff
>     [org/gnome/login-screen]
>     banner-message-enable=true
>     banner-message-text='You are accessing a U.S. Government (USG)
>     Information System (IS) that is provided for USG-authorized use
>     only. By using this IS (which includes any device attached to this
>     IS), you consent to the following conditions:\n -The USG routinely
>     intercepts and monitors communications on this IS for purposes
>     including, but not limited to, penetration testing, COMSEC
>     monitoring, network operations and defense, personnel misconduct
>     (PM), law enforcement (LE), and counterintelligence (CI)
>     investigations.\n -At any time, the USG may inspect and seize data
>     stored on this IS.\n -Communications using, or data stored on,
>     this IS are not private, are subject to routine monitoring,
>     interception, and search, and may be disclosed or used for any
>     USG-authorized purpose.\n -This IS includes security measures
>     (e.g., authentication and access controls) to protect USG
>     interests -- not for your personal benefit or privacy.\n
>     -Notwithstanding the above, using this IS does not constitute
>     consent to PM, LE or CI investigative searching or monitoring of
>     the content of privileged communications, or work product, related
>     to personal representation or services by attorneys,
>     psychotherapists, or clergy, and their assistants. Such
>     communications and work product are private and confidential. See
>     User Agreement for details.'
>
>     # don't show lists of users on login screen
>     disable-user-list=true
>
>     # disable fingerprint reader
>     enable-fingerprint-authentication=false
>
>
> By my count it's 1311 characters, but that's probably not treating the 
> \n's as a single character.  FWIW, this is our approved "short" 
> version of the banner.
>
>
>
> On Wed, Oct 14, 2015 at 3:37 PM, Pat Riehecky <[log in to unmask] 
> <mailto:[log in to unmask]>> wrote:
>
>     That's a bit odd, I've got a 1920x1200 in front of me with no
>     issues. Perhaps my login banner is too short.
>
>     Can I get a copy of your dconf settings file (not the compiled db)?
>
>     Pat
>
>
>     On 10/14/2015 02:30 PM, Sean wrote:
>>     Good point, thanks for asking!
>>
>>     The LCD displays we are running are 24" Hyundai P247D's,
>>     defaulting to 1920x1080, and we're running nVidia Quadro FX 570
>>     cards.
>>
>>
>>
>>     On Wed, Oct 14, 2015 at 3:15 PM, Pat Riehecky <[log in to unmask]
>>     <mailto:[log in to unmask]>> wrote:
>>
>>
>>
>>         On 10/14/2015 02:10 PM, S A wrote:
>>
>>             I just found that I can reproduce the issue using the VM
>>             when I have a 24" display on my desktop and maximize the
>>             VM's window.
>>
>>             Attached are three screenshots of the VM.
>>
>>             Small - banner above the login dialog with scroll bar
>>             Medium - banner on the left side of the login dialog with
>>             scroll bar
>>             Large - banner in column overlaying the login dialog
>>             without scroll bar - this is what the physical machine
>>             with 24" display does all the time
>>
>>             Thank you kindly for your consideration!
>>
>>
>>         Interesting!  What is the resolution of the 24" display?
>>
>>         Pat
>>
>>
>>         -- 
>>         Pat Riehecky
>>         Scientific Linux developer
>>
>>         Fermi National Accelerator Laboratory
>>         www.fnal.gov <http://www.fnal.gov>
>>         www.scientificlinux.org <http://www.scientificlinux.org>
>>
>>
>
>     -- 
>     Pat Riehecky
>     Scientific Linux developer
>
>     Fermi National Accelerator Laboratory
>     www.fnal.gov <http://www.fnal.gov>
>     www.scientificlinux.org <http://www.scientificlinux.org>
>
>

-- 
Pat Riehecky
Scientific Linux developer

Fermi National Accelerator Laboratory
www.fnal.gov
www.scientificlinux.org