With a high volume pump, small
oil pan and cold
oil, the pressure can fluctuate after start-up when the car is moved as the
oil doesn't drain back very fast. I suppose that could also happen with hot oil if the level is low.
The fix for me was to use a larger capacity pan (Aviad) and switch to
synthetic oil after break-in.
With 0.025" bearing clearances and a modified HV pump, I get 85 psi at cold start, 13 to 15 at hot idle and I think about 45 at 2000 rpm when hot.