Their are a lot of vairables to cylinder pressure in a running engine. Dynamic compression ratio concept is that if the intake or exhaust valve is open its kind of hard to compress the air fuel mixture, so its calculated off of when intake valve closes. In a running engine the ramming effect of the air fuel charge affects cylinder pressure, because you can start to compress the air fuel charge against the in coming air fuel charge. I do not agree with the statement that dynamic compression does not mean ZIP. The comment was in referance to running high static compression pistons with a cam big enough to lower the cylinder pressure to run lower octane fuel. But lets look at the same issue from the other end. Put a big cam in a low compression engine and see what you get, a pig that sounds neat but won't get out of its on way. Before I understood better some of these factors as a youger man back in the 70's my freinds and I made this mistake several times. I am not an engineer and not very good at math, but I have used computer engine software to design my engine combinations for many years. Several years ago I built a couple pulling truck engines that were required by rules to run 91 octane fuel. Those engines had 13 to 1 static compression pistons, they one ran good enough to win the points championship that year, and get pulled for fuel inspection, etc. All legal and on the rules. The software I use calculates the dynamic compression and the cranking compression, idle vaccum, as well as the octane requirements of the engine. Knock on wood it has not let me down yet. Last engine I built for pump gas was a 500 cid wedge with 906 heads, for a roadrunner, it ran 10.90's with full interior and all steel body. It had 11 to 1 pistons, and a smaller cam because the owner wanted a decent idle, it had 16 inches of idle vacuum. One thing I will say all the variables to engine design have been pretty much thrashed out by the 1920's We keep revisiting those variables as technology, and materials improve, but the basic theroies all were worked out 100 years ago. Todays engines use viarable valve timing to run much higher static compression ratios and eliminate need for EGR and run super clean as far as emmissions go, so there is a big role for valve events to play in engine design.
