My experience is that this problem goes away when the Editor/OtherEditorSettings/Technology is set to DirectWrite.
Hi, Pecan, thanks. Yes, enable DirectWrite can solve calltip font size issue, but the DirectWrite cause other issue. The main problem is that it will crash if you use C::B from remote desktop. I have report this crash issue long time ago(either in wxWidgets' github or in our C::B forum), it was not fixed yet. Not sure how complex to handle it correctly, the main point is the Direct Draw surface should be cleared once an editor get closed.
My guess is that the font size to window size calculation is wrong here in non-DirectWrite mode for constructing the CC's tip-window.