I def won’t be running dry to find a base level ! My guess is that the residual unusable fuel is there to prevent a run to dry to compromise the submersed pump?
I do find it odd that this confusion exists. Surely a simple option for MMC to determine AND EXPLAIN CLEARLY.
Build a car and add increments of fuel to a bone dry tank. Find the critical volumes for zero fuel pick up to get actual unusable fuel level then add more to find the usable fuel volume to warning light. Forget about the absolute minimum to submerse the pump. Treat that as a type of priming and measure usable after that. It is 2023 after all but not a high tech test that only needs doing once. Surely it would be a pretty important stage during design/development? Ah well.....just keep the tank topped up.
