Sorry if I'm preaching SC101...
probably more for my benefit than anyone elses.

....Negating temperature effects....the SC output to cylinder consumption arrangement is what determines plenum pressure.
The SC pumps it in and the cylinder taketh away. The differential being a residual "inventory" or what we call manifold pressure.
In an extreme example if the cylinders were consuming 20L/sec and the SC was only supplying 1L/sec the residual would be squat.
In our case however....the SC is producing and the cylinders are taking resulting in a pressure of 14.5psig
Change the pulley ratio - obviously changes the plenum inventory...increasing the pump, but the cylinders can only take it away at 370cfm....so the psi in the plenum goes up.
I'd like to do a dynamic model of this...(one day).
Just gotta use a good figure for the CAC/plenum volumes prior to the valves. Might start with 2Litres/quarts....

.....Yes - I'm a time waster.......