...If I still had some air somewhere in the rear, would I see a lower reading at the caliper than the MC?...
My gut says the presence of air is irrelevant. If you have a pipe (container) under pressure, the pressure is the same anywhere in/on the pipe (container). At least for this case, since we can neglect the height difference.
If the pipe was vertical (instead of mostly horizontal), you could add the weight of the fluid pressing on the bottom of the pipe, which would be a psi or so, maybe.
WARNING. SCIENCE CONTENT FOLLOWS. PROCEED AT YOUR OWN RISK.
Pascal's Principle: Any external pressure applied to a fluid is transmitted undiminished throughout the fluid and onto the walls of the containing vessel.