No problem, no offence taken. You’ve answered my question by showing the only fuel you have is the 91-E10 stuff.
I’m not suggesting that you’re wrong about anything, my point was that with the heads you have, at the higher compression ratio, you may have reached the pre-ignition limits of that less than ideal fuel. Lowering your compression obviously solved that issue for you. Maybe better heads & quench would’ve worked as well? Obviously, that all costs money.
I do have closed chamber heads with a decent chamber design , and probably better fuel available than you do so that’s worked in my favour. I agree that using race fuel for street cars isn’t practical at all.