Compression Ratio and Boost Query

I am in the process of a 318 LA budget turbocharged build, and there seems to be a lot of common info suggesting limits of around 6psi boost for an 8.5:1 static compression engine.

I am aware of how timing events affect dynamic compression, and how all things being equal, these principals typically apply to forced induction as well. Anyhow.. I have tried most of the formulas and seen most of the common (and uncommon) charts/graphs.

My question (and what they don’t seems to explain) is this:

I had a 1191 4G63T DSM (Talon/Laser/Eclipse) that ran 15psi on 91 octane with zero signs of detonation. It had no tune, and was bone stock other than a 16G ported and clipped turbo upgrade, along with the cylinder head being decked .0015”. My guess is the decking pushed the factory 7.8:1 compression up to around 8:1. I understand the ECM was likely pulling timing and the heads were fairly efficient aluminum castings. However, that alone doesn’t explain why most ‘boost compression’ charts say that would be a ‘race gas’ engine.

Why can’t I run 15 psi (max) on a properly prepped/tuned 318 with 8.5:1 compression?

Furthermore: If a 6psi limit is true, try finding a turbocharger compressor that maps efficient at such low boost pressures and engine RPMS that meets the potential max CFM demands of a small V8.

Anyone have real world experience boosting a 318 that can weigh in?

Thanks,