I'm afraid this might be more related to GTK than Geany itself, but still...
Most of the computers I use have a 1366x768 screen resolution, and Geany is perfectly usable in them. But one of then has a FullHD screen in which text is too small, so I have set the Windows font size to 150%. Most applications render properly, and also do other editors such as Notepad++, or IDEs such as Visual Studio, but Geany results far less readable than in the other computers, which have 1366x768 and 100% font size.
I'm using Geany 1.31 and Windows 10 (in all the computers).