I realize that RoyalTS uses the ActiveX control when using RDP sessions and not the RDP Client (mstsc.exe) and that doesnt implement the updated protocol settings that newer versions of the RDP client support.
What about implementing something like this in RoyalTS and the ActiveX implementation? Link below:
please check this KB for more information about Royal TS on high DPI systems:
To sum up:
Let me know if you have any further questions.