I've never found that to be true. Cylinder head material has little to do with detonation. I've never built an iron headed engine with less compression or an aluminum headed engine with more compression just because of head material.
I look at the overall package, settle on an RPM range and rough cam timing numbers and then pick a compression ratio.
When the heads come off my current engine I'm going to go up almost half a point to 11.5:1 on iron heads. I'm just a touch over 11 now and I can use more.
