So I’ve done a bleed before but have two questions:

Pushing back the pistons (to get superstar pads in which I know may need a quick sand) they “return” back out a bit even though the system is open both at reservoir and bleed nipple ….why?

When you do a bleed with the bite point adjust wound out I never really get the quick bite I want even with bpa wound back in. I’ve done the tilt tap and top up, but still not great.

Do I need more fluid in system to achieve this?

Sounds like your pistons may be sticking, probably worth stripping the caliper to clean them (and the seals and their grooves)and re-assemble with silicone lube.

I would imagine its the seals settling after you’ve returned the pistons. As Coatesy says maybe need to pop the pistons and seals and give them a good clean out. It’s suprising how much gunk sits in the recess for the seals.