Pump gas compression

No - I think you're just fine. I think you're stopping motion in your head. At peak torque it sure as hell does bleed pressure - but it does it only out the exh port rather than out both ports like it does at idle or low rpm. Plus the "bleeding" action along with the exhaust system evacuation and intake ramming over-fills the available space. So while it bleeds some it's overfilled anyway. So the net change is an inctrease in pressure. But again - the ratio of that volume to be compressed never changes.

cylinder filling % does not = compression ratio which is exactly what I mean. It equals the difference of the cylinder filling as measured by the dyno sensors, and the calculated empty volume - and - that % will rise as the engine approaches peak torque and can remain for rpms after peak torque. It should be well beyond 100% VE at peak torque.

edit - this is all assuming that the engine in question is built properly and has no inherant detonation or preignition inducing features and is being run on the proper fuel.