@Khaled - I have updated my dialog to use the new x y w h values for "map" and tried it at 100% and 150% scaling, and I am pleased to report that it scales pretty well wwhen using "map".
So we now have two alternative solutions:
1. If the dialog uses dbu then you can use mIRC compatibility settings on Windows 10 1703 or later to make the dialog scale properly.
2. Or you can switch from "dbu" to "map" and adjust x y w h.