Concerning the háček...


I have a couple of questions about the háček and, whilst I'm sure the answers are buried in the forums here at typophile, I cannot find them.

I know that for the /d/, /L/, /l/ and /t/, the háček takes an acute-type form. What I can't seem to find a consistent answer to is the question of what form the háček takes with the /h/, /I/ and /k/. The háček article at doesn't mention these other letters, but other online sources seem to suggest the háček is placed directly above the stem. Is this correct?

As a subsidiary question, what are the implications for the font metrics if it is placed above? For example, if my font currently has an EM Unit Size of 2048, would it be a problem if a vertically stacked háček forced my Ascent value beyond this?