Thanks, Ernst. I believe we are addressing two different things.
1. The tilt flow testing will address suction and usable fuel elements. In that test it is best to have a high flow rate. The highest flow rate will be at low resistance to the boost pump output (pressure). If there were a high suction resistance then the delivered fuel would contain bubbles, of not be able to deliver the fuel because of cavitation (vaporization) of the fuel prior to the boost pump. This test is definitive. In the usable fuel range, 200% of rated flow is excellent for evaluation of the system to the pump.
2. The OP is addressing the delivery, at a specified pressure. Having passed test #1, then the boost pump must deliver 125% of maximum fuel flow, at pressure, necessary to keep the engine running. That might be 5 psi for a carb or 22, 25 psi for the fuel injected engine (I don't know the exact numbers). The exact numbers can come from testing the engine or the specifications sheet for the users specific engine.
Thanks for your response.
Comment: The list of what we might call "installation tests" is not totally clear regarding what is being validated and why. The fuel system presents some mysteries for people and could relate to fuel system related loss of power or reduced power. Some of these tests have have pressure/flow margins built in to allow for elevated temperatures that might occur a few times each year or less. Tests are necessary since all of these factors are different in our individual planes as components, routing and configuration are changed from a baseline (factory) configuration or are left to the builder to decide. Someday, maybe a full list of validation procedures will be made for experimental that will address the whats and whys, and how to. For now we just follow instructions and muddle through.