RE: muzzleloader scope
I don't believe you can "move" the circles.But bigmossy is right otherwise as changing magnification will produce nearly the same results as moving the circles. At 9X, the distance between the center reticle and the first BDC cirle or line might be (for example) 4" AT THE 100 yard TARGET. Reducing magnification by exactly 1/2 would result in that distance (at the same target) being twice as much or 8" in this example.
Just as field of view increases as you reduce magnification, so does the amount of span between those marks increase (at the target).