freetypy.TT_VertHeader.ascender

TT_VertHeader.ascender

The font’s ascender, i.e., the distance from the baseline to the top-most of all glyph points found in the font.

This value is invalid in many fonts, as it is usually set by the font designer, and often reflects only a portion of the glyphs found in the font (maybe ASCII).

You should use the Face.get_os2_table().sTypoAscender instead if you want the correct one.