Patricks car above is a good example.
The sender gets doused with hot
oil leaving the crank,cam,heads draining etc BEFORE the
oil gets a chance to be cooled off in the pan.
Reading near the bottom of the pan is as cool as the
oil could get prior to the oil being picked up again by the oil pump.
Just like a coolant temp sender is fitted at the hottest part of the engine prior to the coolant going to the radiator, the oil temp sender is best located as like Patricks or my case as above.