Thanks for reporting. At this point, fixing this issue is going to take several hours of work, so I don’t have a quick answer 
It’s not just including the in-game render scale in calculations, it’s actually way more complicated than that and has to do with the way we intercept the game’s call to prepare for rendering.
I’ve filed the issue on GitHub indeed and you can follow the progress there when we get to it!
One thing that worries me however, is that in-game render scale and the lower resolution does not play well. Even if we make it work, you will be getting a lot of nasty visuals, like this:
Maybe you can try now by using a more reasonable in-game render scale (like 90%) and see how it looks? Because if it’s going to look like the above, I don’t even want to spend time fixing the bug