some ring leakage would be normal or how could you get blow by ?
piston heads get hotter so they would need to be smaller.
You said that you replaced the head, did you do a leakdown test to be sure a valve was not leaking ?
add a little oil thru the plug hole, if psi goes up it is rings, if psi stays the same it is valves, same test for checking compression in worn engine, assuming everything else is correct.
just an idea.