'I can't visualize that but I'll take your word for the loop. As an explanation, if you use a standard filter and the plug up in the block above the pump is in place, that will help keep oil in the system below the pressure sensing point, for at least overnight and maybe for some days, depending on how well the 'flapper' anti-drain back valve in the filter seals. That is the main system design feature to keep things primed. You can't prevent the oil draining out of the system much beyond that point, once it starts 'downhill' to the mains.
