i did not realise that the pressure sender location was so critical, always learning
It's not, really. Well it isn't in most engines, I don't know what engine you're working with. There's basically two "zones" of pressure* before the oil reaches the bearings: after the oil pump but before the filter, and after the filter but before the bearings. The difference, as I said, is the pressure drop across the filter media/bypass valve. The drop can be substantial while the oil is cold, one of the reasons there is a bypass valve built in, but once warm the measured drop is only 2-3 psi. Not enough to be concerned with, if your view of gauges is like my own that they are relative, not absolute, indicators.
*[I'm excluding Type 1 Aircooled VW engines, which use a single valve to act as both a pressure relief and as a diverter to the oil cooler circuit, based on the lowering viscosity with increasing temp. These will show greater differences in pressures in the different circuits, but even so, the differences are not large. And of course those engines don't have a full-flow filter, so the filter pressure drop is also not involved]
