I'm testing out fractional scaling on 19.04 and unfortunately it has come up short with X11.
It seems to work OK on a single monitor, but when plugged into a second monitor (and I've tried two different ones with the same result, one via hdmi the other display port) the second, larger monitor get set to the correct scale by the looks of things but it cut in half (or less) with the other half being black and the desktop not extending to the edge of the monitor (if that makes sense).
I'll test on wayland now. Hopefully that still works as it did under 18.10.
After enabling fractional scaling on wayland, this is not an issue here, scaling seems to once again work correctly.