The slot is an
exact fit over the post so it cannot move from side to side (ie. radially). It will move a tiny bit from center to the outside if the encoder is not exactly centered on the point of rotation (which of course is the ideal) making sure no pressure is put the encoder.
The powered ground board kit makes no difference to the balance as it is all in the rocker box and ground board. But yes it is important to know the weight of the optics and all the other bits and pieces. This determines the size of the side bearings in an ultralight design. You want the center of rotation of the bearings to be at the scope's COG. Also, these larger bearings can handle more variation in changes of weight in the top end. In the Obsession type you just pick a bearing size and fine tune the balance by moving the mirror cell up and down, then trimming off the bottom of the mirror box to suit.
Fun fiddling with ideas isn't it.
