Exhaust back-pressure Q on simple 2-stroke yard-equipment engines:

I am having trouble getting a precise answer- is back-pressure necessary on a little single-cylinder 40cc 2-stroke like a chainsaw or a blower? I ask because people frequently modify mufflers to increase flow (which does work, basically just ‘defeating EPA restrictors, sometimes its literal plastic tabs blocking fuel-jets 😛 ) but there’s always someone who’ll bring-up back-pressure and how some unspecified amount is of benefit to this type of engine. I’d think not (since the impulse-line is the ‘cyclic back-pressure’ of the system) but wanted to know for sure before modifying a muffler on a brand new / high-end saw 🙂

PS – on these types of mufflers, in theory, can anything travel inward to the cylinder via the exhaust port? For instance I noticed I’d left my saw on a dusty pile and its exhaust was creating such a dust-cloud around it that, if in-between that rapid up&down of the piston, if air(and here, dust!) can travel inward through the cylinder’s exhaust-outlet port, I can picture both Yes & No because there’s gotta be suction on 1 stroke but hard to picture that pressure is equalized via sucking-in-air through the muffler!
If in normal operation, a chainsaw/blower takes in nothing (via exhaust-port) while operating, and backpressure is irrelevant, that’d mean ‘optimal’ was no muffler & that mufflers for optimization would be built so they could muffle as much as possible w/o restricting flow — a tall order for non-engineers but some muffler is quieter than no muffler and these things scream regardless..
Thanks a lot, have never done a muffler on a saw as-important as this guy so really wanna ensure I’ve got the principles down right, going to braze a tubular pipe onto the rectangular muffler and would certainly braze a mesh-screen into it if I knew solids could potentially find their way into the muffler in some odd circumstance / weird cutting position!

[PPS – I know “It’s naturally aspirated ergo compression is king” but the type of block in this saw doesn’t allow changing floor height so porting the block itself is of little use, only advancing the flywheel’s ignition-timing and increasing muffler/air-intake throughput can give boosts so want to ensure I don’t do something that’s causing as much harm as good or doing something unknown that I’m missing!]