Yes I understand, there is a lot of lowercases that have overshots on top, but there is Ascender metric for that. I posted that screenshot (with very high ascender and even without overshot zone size) just to highlight the behavior for others who may not understand what you are asking for.
When Ascender is the same height as Cap Height, the solution would be just set both values the same. And then the brown zone size will be shown for the lowercase ascenders.
I was worried about zones conflict when setting the same positions (for example 700) for Ascender and Cap Height. Just one thing in this case is the Cap Height zone size should be set to 0. Just checked and after the OTF export there is just one zone survive on 700, without duplication.
In Fontlab, Ascender value locked with Typo Ascender, and according to the Webfont Strategy it should be set much higher of an actual lowercase ascender – somewhere on Uppercase diacritics. That’s why some fonts use Ascender value not for actual design of lowercase ascender.
But in Glyphs there is separated custom parameter typoAscender for that. So Ascender metric can be finally set for its original purpose – to fit the design of lowercase ascender, with a size for overshot.