My setup for my day job these days is a Surface Pro 4 and either an LG 34UC87M-B or a Dell P2715Q monitor, depending on where I'm working. This is a fantastic setup, but some applications have trouble dealing with the high pixel density and don't scale appropriately.
One case in point is Skype for Business. For some reason it scales correctly as I move between the Surface screen and the external monitor when I use the Dell, but on the LG monitor Skype is either massive on the external monitor, or tiny on the Surface screen.
After a big of digging around I came across a solution that worked for me, which is to change a setting in Skype's manifest file (who knew there was one?). On my machine the file is here:
C:\Program Files\Microsoft Office\Office16\LYNC.EXE.MANIFEST
And the setting in question is this:
Which I changed to this:
Note that you'll probably have to edit the file as administrator in order to be able to save it.
Once I made that change, saved the file, and restarted Skype, it now scales correctly for both the Surface screen and the external LG monitor.