Dear Alex,
I don't know how much you know about Basketball and rebounding, but again, height is not the major factor in rebounding skill! If a Dwayne Wade is able to box out and bump away a Shawn Bradley away from the rim, he will take 5 out of 6 rebounds in a match up against him. To Rebound correctly you need Orientation, Reaction, Stability, and Skills like Boxing out, Bumping, Jumping, Catching, Landing.
And if two equally skilled players meet each other, again, height is not the mmajor factor, as all the skills mentioned above will be the same on both players, so therefore it would be a 50/50 chance who gets the rebound. But I can not imagine two players being EXACTLY EQUALLY SKILLED in all areas, so there must be something that favoured the smaller guy to take more rebounds than the big guy.
PS: Pau Gasol is a very skilled player. I don't see the comparison to Charles Barkley, because Pau Gasol is a great and intelligent player. Of course Barkley would be less effective against Pau Gasol, but not because of the height of Gasol, but because of his SKILLS.