RE: 8.8X9.75 @ 19,300+ !
You probably do not have to touch a thing......... it is likely running at a pipe harmonic.
As long as the needle is easy to adjust and set, leave it alone.... fly it. If the needle is over-sensitive or the engine gets hot, then yeah, the pipe is short. Sounds to me like it runs well....... so leave it there.
On the right plane, that prop will unload a ton in the air.
Don't read anything into the over-square stuff too much, and static thrust does not mean squat unless its for take-off acceleration or hovering. Props are designed for flight - dyanamics.
Bob