...The situation with the oil pressure happens from all the restrictor/bleed down points between the supply (main gally right out of the oil filter) and the final destination. This motor doesn't make a lot of total oil pressure to begin with (the manual specs 45-ish psi @ 3500RPM iirc... the ZX14 I just did made 90psi @ 11000 RPM)., so multiple restrictions and bleed downs have a big effect. The main bearing at the rear is one bleed, the rear piston squirter is another blled, then it travels up the rear of the block to the banjo bolt (restriction), then the cam girdle (bleed), and then to my sensor.... which has a bleed right after it in the form of a turbo oil feed. I have the sensor essentially where the stock switch was, but outside the fitting after a .125" or so drilled passageway. The turbo doesn't really need much oil, so I'm not worries about that, but having a bleed on the same side as the sensor isolated by all those restrictions lowers the observed pressure significantly.
All that said, I'd like to see more than 45-50psi at the main bearings on something that turns 8k+ rpm. I've been shimming oil pump relief valves for years... just forgot to do it on this one, and you have to split the **** cases.