I just added a small message to the Video Options menu letting players know how to get UI scaling to work.

The whole system is still a bit of a hack, so I am reluctant to make it the default method of using Full Screen. I am not saying I will improve upon it, as I am not sure exactly how to fix some of the underlying issues. I am also reluctant to make any major changes to the way resolution works. It is far from perfect, but changes have a tendency of causing a lot of unforeseen consequences, and I would prefer to keep things working for the majority of players as it stands...

There is a more in depth discussion about resolution and how it works here, if that helps anyone:
https://steamcommunity.com/app/502720/discussions/0/5401527630819996792/