I am not sure if this is just a quirk of Apple’s rasterizer that Glyphs cannot do anything about, but when I try to adjust vertical metrics by setting custom parameters like typoAscender, it is ignored at least on Apple apps (like Font Book and TextEdit, on OS X 10.11.6) and the line gap becomes larger. I noticed that the presence of, and the shape of the glyph Agrave affect this. The attached file shows this phenomenon.
LineHeightTest.zip (19.0 KB)
If the actual glyph shape of Agrave extends above the ascender height, that height overrides the vertical metrics, it seems. In the attached Glyphs file, if you swap the glyphs Agrave and Agrave.001, latter being shorter, the line gap gets smaller. Other glyphs like Aacute don’t show this kind of effect.
In FontTableViewer, the vertical metrics look fine. I do not have other rasterizers to test such as Adobe apps.
My current workaround to this is to make the default glyph for Agrave (U+00C0) short, cutting off the extending part of the diacritic, and use the calt feature to always replace it with a more properly designed glyph. Is there any way to fundamentally solve this problem?