Just to be able to reproduce before sending a fix: what are your settings?
I guess you’re on a high-DPI monitor. E.g., you told me it’s a full HD monitor, but I guess it’s on a small display (e.g., 13” laptop), so you use some system scaling.
When I tried my patch, it seemed to work well even with scaling, but I tried on GNOME.
What DE are you using? And how do apply the scaling? With a settings UI, or with xrandr? Are you on X11 or on Wayland?
I’d like to test the patch in 16.0a1, because I fear it’s a bit too late for 15.0.3 (we would like to build it soon to release tomorrow, sorry).