I disabled UI scaling on Accordance, ansd it didn't resolve the issue. I also bumped up the scaling overall on the OS to enlarge everything, and the toolbar is still tiny. I've talked to other developers who are having UI scaling issues on Surface Books, and I'm told developers can rectify it on their end, but it definitely takes some effort (WeatherBug is one app that is horribly tiny on High DPI screens; I can't even read the weather text). When I discussed this with my teams at WeatherBug, they said they can (and will) rectify it in a future update.
99% of the Accordance UI is OK. Zones and module UI is decent, so is text, etc. It's the toolbar that's just tiny. If Accordance can add a "larger icons" and "larger toolbar" feature to Accordance (even in 12), I'd be thrilled. That's the one area I'm having major issues with because the icons are "that" tiny.
That or I need to better learn how to use keystrokes so I could hide the toolbar. ;-)