All my masters have the same capital height. When I use autohinting, my TrueType fonts within the family show different uppercase heights. How is this possible and how can I prevent it?
See, for example, sizes 17-19 in the screenshot. The heights actually differ in almost all sizes.
ttfautohint has an option to orient its zones after an existing TTF. Effectively an equivalent to family zones. @harbortype pointed me to this the other day. It is not in the UI though. But you can add it to the custom parameter value.
But how to implement it in Glyphs via a custom parameter?
You should be able to add it manually to the value string of the custom parameter. I’ll have a look if I can add it to the ttfautohint script.