Thanks for the link.
If there really IS standardisation on glyph numbring, this would help.

I am currently thinking of a hybrid system, in which the program would automatically switch some characters (but not all!) back to the draw version at small font sizes. That wouldn't be too difficult, as I haven't yet taken any of the code out.

There are particular problems with rests for quavers/8th notes and shorter, which just show as blobs on the smallest size.

I imagine that the problems are mainly due to screen resolution, and that for printing, the fonts are better at all sizes. Unless I am careful, this could cause WYSIWYG flaws though, if the drawn character is slightly different in size.