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.
How?
With a ‘blue zone reference font’:
https://freetype.org/ttfautohint/doc/ttfautohint.html#blue-zone-reference-font
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.