My biggest problem with this is that you're not using ligatures defined by the font to perform the hinting required. If you did use ligatures - derived from th

My biggest problem with this is that you're not using ligatures defined by the font to perform the hinting required. If you did use ligatures - derived from the typeface itself - then the hinting of the underline cuts can be better fitted to the face. But that assumes that the type designer themselves considered the case. So .. to me .. you're patching something upstream which might be better considered at the source: the font itself.