Combustion chamber shape gains are more significant than the actual compression ratio, especially in a 2 stroke and even more when you get around to to tuned pipe. The stock head has a terrible squish area. Squish is the area that is closest to the piston and is important for developing turbulence and increasing burn speed while fighting detonation.
Here is a corny sketch of how it works:
I modified my stock head to push the squish area out to the edge of the cylinder and have it match the piston.
The squish gap should be 0.5mm to 1.5mm, ideally 1mm.
The advantage of this shape is less detonation and heat regardless of the actual compression ratio.
Excuse the poor photo quality. Head on the right is the modified one.
Your Hi-Comp head should have this shape.
Check the squish gap with 1.5mm lead electronics solder. Rosin core is OK.
Solid mount the engine. I have been through this with motorcycles and quads.
The more points of contact the better.
Get a better air filter. Right now.
I have only 300 or so miles on my China Girl and just discovered dirt is getting past the stock air filter and scoring the cylinder.
Steve