Ok, I got to the root of this… and it looks like the others got this right by messing with the DensityDPI setting.
The problem is that Android source code (I checked latest) has a mechanism of detecting phone mode, which is: smallest size * 160 / densitydpi – if that value is < 600, you are considered a phone, and Roon trusts the OS.
This device, being 10 inches diagonal and 1280x800, should have a DPI of ~150, as per https://www.sven.de/dpi/
The problem is it is reporting a densitydpi of 213 (TV). If they really wanted to stick to the Android steppings, it should be reporting 160 (MEDIUM).
If they did the right thing, Roon would want to run in tablet mode (landscape). But, because of this stupid setting, they are making your 1280x800 tablet feel much more like a 960x600 tablet 
NOTE: I also speak to the technology in Android behind all this here:
https://community.roonlabs.com/t/where-is-alphabetical-navigation-in-android-client/13659/21