On the point of nose down fuel pickup in a modern pumped YS engine F3A aerobatic setup we rely on two things.

(1) Engine power is usually set to indle in a downline so fuel draw is at a minimum, a 45 deg downline might (?) carry a slight bit of power depending on your setup.
(2) The "clunk" is covered in an absorbent foam which blocks bubbles AND holds a certain quantity of fuel to prevent air being drawn into the line while the clunk is out of the fuel.
.....(3) there are also tanks with a bladder in them but they're rare F3A now.

Now if I were a beginner and flying my trainer with unpumped engine around all day, tank height isn't super critical but if I were flying something which I expected to be pulling sustained high levels of positive and negative g's I'd put in a bit of effort to get the position correct. Even flying F3A I'd only be be pulling sustained (~2-3 seconds) 3g's worst case (except for snaps) so that +1 inch head becomes a +3 inch head and -3 inch. I'd expect sport flyers would be pulling much higher g's for longer periods. eg a 4 sec loop at 130km/hr is about 6g. Pylon racers would be up in the 40+ g so a few millimetres in tank height is critical.