Having to live with the design decisions that you make.
I have decided from the start to make a light weight 10" high mirror box.
Using the spreadsheet provided by the Albert Highe "Portable Newtonian Telescopes" weighing most of the components x distance from the bottom of the mirror box points to a 15" radius for the Alt Bearings. This is the distance from the Balance point or M point to the bottom of the mirror box. Other methods of balancing the scope outlined by Krieg and Berry indicate that the secondary cage is going to be much heavier than the mirror box when distance weight is calculated.
So I am going to go with a 17" Balance point. Actually a 17 1/4 to allow for the teflon pads.
The second decision to make is balancing the clearance of the mirror box with the bottom of the rocker and how deep to set the box inside the rocker. The first is easily achieved by a scale drawing on graph paper and a compass. The second decision is dictated be requiring at least a 60 percent arc from the M point, (30 degrees either side of the middle of the box) to space the teflon pads.
Now time to pause and think about it before making saw dust!!
Here is my marking out of the two rocker sides. Used a thin MDF stick compass to create the arc.