I asked this very question of Bob Brassell from Jett Engineering. I was looking for a 26cc tuned muffler at the time. He said that they had looked at it, but ruled it out because a tuned muffler that worked on a 26cc gasser will be nearly as big as a canister muffler and that in the gasser market, most users were more concerned with finding an in-cowl setup than max power. A tuned muffler would never fit in a cowl and would be cosmetically unacceptable to many gas fliers.

I think what you want is a good canister setup, it is much shorter than a pipe, can be very quiet and makes way better power than any in-cowl muffler setup. Done properly, a canister system will equal or even exceed open exhaust power levels.

Mark