Got a LEO .46 (think of it like an OS) with a 10x6 prop on it.
The engine loads down too quickly. There's no noticeable sound difference from ~70% throttle to full throttle.
Increase the pitch?

It depends on what your flying, you may have to do some experiments to find the ideal prop for your application. Some props that would work on that motor would be 10/6,10/7,10/8,11/5,11/6 etc. Your not going to hear much of a difference anyway but a 10/6 on a .46 is a little small.

"Engine loads down too quickly" may not be what's happening.

A 10x6 is an excellent choice for a .35 size engine. I run 12x6 props on my OS46AXs, OS45s, OS46FXs. They work ok. Also have some 12x5s trimmed 1/2". They work great. The 11.5x5s work better than the 12x6s. Both props push LOTS MORE AIR than a 10x6 would. They really ought to load the engines way more than that little prop would. And the little 10x6s are probably "spinning their wheels" in most situations where you'd like the prop to be pulling the airplane more.

I'd bet the engine is actually not loading at all after that 70% throttle. It's running it's guts out and has no more to give.

Try an 11x5.
Don't expect to hear higher rpm.
Adjust the needle to see some exhaust trail in flight.
Then try a 12x5 or 11x6.
Adjust the needle same way.

Don't judge the airplane flight by the sound but by the performance.
Try this test of each prop, including your 10x6. Full throttle, level flight for at least 3-5 seconds. Pull into a straight vertical. Count how long the airplane climbs. Now try the next prop. etc

The problem may be the silencer [ muffler ].

Some Leos have a very restrictive silencer. If thesilencer is a small single chamber unit try a 10x8 or an 11x6.

I assume you mean that by "loads down", the engine RPM does not increase over 70%. This signifies a prop that is too large or has too much pitch or both. Try a 9.5x6 or 9.5x8 and see what it does.

Dr.1