I basically agree with Ed. This is torque roll and because you don't have chassis flex is why you see it.
Any real pinpoint help as far as setting go would be in the crystal ball area of chassis set up, but with some good guesses I would start by dropping rear ride hight about a half inch in the rear and putting a very little preload on upper right bar. Say about a 1/4 to 1/2 flat shorter, and see what you have. If you still get roll add more preload. when it levels out look at compression or separation in rear. You want neither.
While Torque roll in it's self doesn't indicate better traction on one slick over the other, it will change the IC from side to side and that could and will change pressure on them contact patches.