Looking from the front of the buggy imagine a vertical line in the middle.
say your center of gravity is the height of your gearbox and your roll center is at the bottom of the gearbox.
Those two points are your "roll moment" the bigger the roll moment, the the more it rolls ( i use that for slick surface)
So putting the rear top arms to the top hole makes them parallel to the bottom arms lowering the roll center giving you a bigger roll moment, which is the angle you need for max roll.
If you move the top arm down they are no longer parallel and your raising the roll center closer to the center of gravity making the roll moment smaller, so doesn't roll as much ( less chance of grip roll on high traction like boring asto turf).
The length of the top arm comes into play changing the camber gain and the rate it rolls but thats another story
If i'm wrong please delete this post , i wouldn't want to steer anybody
wrong.