The power characteristics of a 2T engine is largely determined by the port timings and other factors like compression ratio etc.
Once that is established, the expansion chamber is then designed to match the specified engine characteristics.
Tuned lengths, match the RPM range that the engine is design to operate in.
So, having a longer pipe for low RPM, on an engine with port timings designed for higher RPM, will just result in a mismatch and less power.
The shape of the disffuser and baffle, likewise, have to match the range of power the engine is designed for.
Saying that......You might get lucky, and blindly improve on a mismatch that presently exists, as it is highly unlikely that standard TSR EVO is expressly designed to work with your present engine characteristics anyway.
good luck.