When should the word mid be hyphenated?

Generally, hyphenate the "mid" (within, in the middle of) prefix if it modifies an original Word as opposed to a distinct term, and for items that do not have separate "ends" or "middles". e.g.

midday, midair, midway, but mid-sentence, mid-ocean, mid-Atlantic, mid-stride. Also, if the resultant Word appears indistinct, such as "midriver" (readers see the Word 'driver'), hyphenation may clarify the intent.