Tsiklonaut, as I recall you mentioned having a very high-compression head. One would think there is nothing simpler than a 2T head, right? But the devil is in the details. Small changes in squish clearance and/or blend radius (from bowl to squish band) can have a large impact on squish velocity, which in turn can have a large impact on rate of combustion and therefore combustion pressure rise versus crank angle.
I always try to keep in mind the words of a famous racer and tuner, Kel Carruthers: "Give the bloody engine what it wants, mate."