On Windows10, I use the 'Customise your display' option for 'Change the size of text, apps and other items' to increase the size of apps on screen (mine is set to 150% - the default setting for my display according to Windows 10 is 100%).
I find this makes Sonar much more useable with a touch screen (yes, I lose some screen 'real estate' by enlarging everything, but at 'normal' size the touch screen isn't very useable).
 
However, I've noticed that if I insert the 'TruePianos Cakewalk' VST into a project, it reverts the screen display bak to 100% scaling (and I have to close down Sonar to revert back to 150%). I assume there's something in the VST code that 'breaks' the screen scaling settings...
 
Has anyone else come across this issue?

For anyone else looking at this in future, these are a couple of excerpts from a response from TruePiano support:
 
TruePianos currenctly doesn’t support scaling of it’s GUI......
 
......As for adding scaling support. The bundled version will only be updated when we receive a request from CakeWalk/Roland for this. We provided them with an update in the past which they didn’t use since from their perspective nothing was broken and they wanted to avoid potential issues due to including a different version of the plugin. As for adding scaling support to the full version of TruePianos. I cannot say when this will be added I fear. I agree though that it requires some priority with today’s high resolution displays.
 
I was looking at possible options hosting TruePiano in a separate VST host (such as SAVIHost) and connect Sonar to it using LoopBe or a similar internal midi routing software. But this isn't possible because the VST that comes with Sonar is 'locked' to only run within Sonar :(