You would need some pretty sophisticated instrumentation and time/testing to fully answer all of your questions. Vacuum is not always easy to quantify in terms of what is actually going on, especially since in the practical world of CNC routing, things are not always linear.

One possibility regarding less than 4-zones, could be that there is enough leakage (and there should be SOME for cooling of these motors) to move the working vacuum characteristics into a different area of the compressor trim map. This is akin to a turbocharger compressor map - and while ideal is linear, actual is not. Plus, unless you are running a completely sealed setup with gasketing, there is going to be some leakage, such as around the table perimeter, or if you didn't do such a hot job with the plumbing.

Static CFM is very much relevant during the initial suck down when the pump is beginning to build negative pressure - aka getting over the hump. For example - you may have one of these motors capable of 100 CFM static and an air conditioning pump that only pulls 5 CFM, but maxes out at 27 Hg". That pump will NEVER build vacuum without properly sealed and gasketed fixturing. It just doesn't have enough CFM to seal things off. This is where a check valve makes sense in conjunction with a high CFM vac - especially if you are doing something like vacuum bagging. Big CFM vac to remove most of the air; small high suction vac to pick up where the big CFM pump left off. Neg pressure pulls the valve shut & big vac can be turned off.

The thing to remember with these vacuum systems is that they are designed to be a shoestring solution to more expensive vacuum pumps. The original idea was to employ these bargain setups and make some money until you can afford a proper commercial/industrial grade setup. Some users don't have 3 phase or simply can't afford (or don't need) a pro setup - so certain provisions and allowances have to be made...as in, 'you get what you pay for' & 'everything has a price'. So...some questions probably cannot be answered without either paying someone to do the research/study or you have to do this sort of thing yourself.

-B