Yakes!!!! the old HP (high rpm's)verse Torque issue again. I don't know of if at 3:30am if my brain will work well enough to describe why a slower turning 4C swings a larger prop. Due to the way a valved engine is (timed) you get a vary different fuel burn time causing a higher CYL pressure(not to be confused with a high compression ratio) this high Cyl pressure (torque) can turn a larger prop.

See my brain already forgot piston Stroke length and plugs heat ranges(changes the burn time)affecting the CYL pressure/ torque curve..........I'm going to BED

Good night checklst

Spaceman you are a fast typer your post was not there when I started my brain dead post.......LOL