How/Why does sommelier scaling work?

[ZiemlichUndead]

I am using crouton with focal fossa via sommelier on an arm chromebook (Lenovo Ideapad Duet). I know fossa is not officially supported but as far as all my tests have concluded, it does a lot of things better than xenial.

My question is whether anyone can tell me how and why sommelier windows scale the way they do.

My native screen resolution is 1920x1200.
When I set scaling in ChromeOS to this native resolution and use --scale=1.0 in sommelier options, my windows are correctly scaled.
But when i check what resolution my linux programs think they are running ("xrandr" or "xwininfo -root") I get a resolution of 3413 x 2133 as a result.

Now, when I change my chromeos scaling to for example 1440x900 while not changing sommelier scaling, my linux programs get blurry and xrandr reports 2559 x 1599 as current display resolution. I need to get this reported resolution back to the initial 3413x2133 via sommelier scaling to get a sharp image. In this case, the correct value is --scale=1.3336 (Which I found out through brute force testing).

Why is sommelier behaving this way and why are my programs scaled perfectly to 1920x1200 while they think they are at 3413x2133?
I mean, I do have sharp programs and no problems with this configuration, but I really would like to know why this all happpens.