There is no 2-layer gasket, they are all 3-layer!! Thats a myth!
The oem gasket will be compressed when instalt to a size of 0.028''
The P2H clearance of my z6 block / z1 head is 0,5mm / 0.02'' with a compression of 11.3:1 (head milled .002'')
I'm running 95 ROZ gas/fuel with 19-20:1 AFR till 4000rpm at part throttel and 16:1+- when the 2. valve gets activated.