06DB threedotsabove-ar is a combining mark that was added to Unicode to represent the small high three dots (hence the name ARABIC SMALL HIGH THREE DOTS), which is distinctly smaller than the three dots above seen in letters with three dots like 0634 sheen-ar, etc.
Designing or using 06DB threedotsabove-ar to compose the letters with three dots like 0634 sheen-ar, etc. is wrong.
@GeorgSeifert 08A7 meemThreedotsabove-ar should not decompose to “meem-ar, threedotsabove-ar”, none of the three dots letters should use 06DB. It would be better if 06DB had “small” in its name.
@ahmattu FBB7 threedotsupbelow-ar, FBB8 threedotsdownabove-ar, FBB6 threedotsupabove-ar, FBB9 threedotsdownbelow-ar are useful, since they are in Unicode. You may not want to add them to your fonts, but others may do so.
They all can also be used as components, including in the letters that have three dots above pointing down or three dots below pointing up like 068F dalThreedotsdown-ar or 0764 kehehThreedotsupbelow-ar.