I have the Bigfoot leveling system. It was installed by Bigfoot themselves.
I was going to have them install the Snap Pads but they came back to me and said I was at the Minimum clearance and suggested I DO NOT install them.
Rear is 8" and 29" behind rear wheel. The front are 7" and 20" behind front wheel. Measurement taken from the center rear edge of tire (not the bottom as you described)
I took into account the distance behind the rear wheel mostly due to the drop when the rear wheel goes into a type of dip in the road, like when you go into gas stations that have a drainage area between the road and street causing your rear end to scrap. This can affect the levelers also if too low. The further back from the rear wheel, the more the chances of bottoming out.
Side note: I took a straight edge from the bottom of the rear tire to the bump stops just in front of the rear bumper. I found the reason why my stabilizers got bent. They were installed in front (and below) of the stops, so it will hit there first before the stops. Great designing Thor.
It is me I'm sure, but I have no idea what you mean when you explained the departure angle. Sorry!
I did find this though.