I tried to find to find where characters like »ḋ« are used and so far the only thing that came up was traditional Irish orthography. It seems that for this purpose the preferred position for the accent is at x-height. (The picture is just an example I found.)
However, most fonts place the dot accent higher.
Is there another use for these characters? Or is it safe to assume that the dot accent should be placed at x-height? Thanks!
Generally, there is no obvious reason for handling the dot accent differently in design than the other tittles. Keep’em in hight adjusted with acute, grave, tilde and others. x-height isn’t exactly the propoer term for that. In detail, much depend on the design of the specific face. According to my experience I find it rather disturbing when an accent is placed much higher than on the average position in the font. Accented glyphs with an ascender are a special case though. Your example shows well how it can be dealt with.