Roger, did this work, please?
I will be redrawing old FOG 4.1 font designs from scratch. (I can't find backup files on usable media I still have.) These, of course, included accent marks over vowels and so on, as you describe.
My understanding of how fonts are designed was that yes, accent marks on capitals and lowercase may often go above or below the stated em-square.
When I had, back then, looked at other fonts to see how they were produced, the accent marks might add to the total em's 1000 units to reach as much as 1250 or so. So I presume this is the standard practice in font design.
The alternative would be to scale everything down, which then makes stem weights and glyph heights and widths some very odd, inconvenient values, and results in what amounts to built-in leading of about 120% to 125%. This seems undesirable and unintended, and from what I could tell, not usual practice.
Advice would be appreciated. I'm self-taught.
Oh, if only I could find a backup somewhere in a storage medium I can still use. (I think it's all stuck on things that I can no longer access, or else those backups were lost in an old hard drive crash or two, many moons ago.) -- So I'm expecting to have to redraw what I had done back in the 1990's. Sigh. On the other hand, redoing it might be good practice and better for the ultimate design.