Yes, all the above will vary the results. When comparing comps, we compared apples to apples. So, we used the same 16 inch M4 barrel, ammo, etc. The only thing that changed was the comp.
The recoil energy will most likely always be the same if using the same ammo, no matter the rifle weight, ammo, comp. But, if the rifle is heavier, you will perceive less recoil. That's because that same propellant energy blast gets used up moving a heavier weight, so it will feel lighter to you. On the other hand, if the rifle is lighter, you'll probably feel more recoil. There are lots of factors that influence recoil.
All we are saying is that if all the other factors being equal for each comp under comparison, the HIPERCOMP 556 will reduce felt-recoil the most.