This is a follow up to my previous question, about a seemingly unresolved "suspension" in Bach's Prelude in C major, bar 21:
In the next bar, it resolves to this chord:
If we block the chords, we see that the upper and lower voice move in stepwise contrary motion, from the very dissonant major 7th to the imperfect consonance of a major sixth. I was under the impression that resolution of dissonances in this style was strictly limited to oblique motion(one voice moves to meet the other in consonance, the other remains stationary), but that evidently isn't true. I can't seem to find anything on this topic. Bach has shown that this style allows for resolution of sharp dissonances via contrary motion, but can we do the same(assuming free composition, rather than strict counterpoint) with similar motion, and what are the guidelines surrounding this kind of resolution?

