I have not found anything on the internet in the way of a dimension that will help us.  I, too, find myself guessing.  So, what I am proposing is a test that would make me confident that a 1g bump to the stops would not result in tires rubbing, metal to metal contact, or coil bind.  What I intend to do is mount the bump stops to a bracket that leaves at least 1/2 inch clearance between the frame rails and the top of my half-shafts.  Your situation may be different as yours are a smaller diameter than mine.  Then I am going to place the weight of the car on the rear suspension with the coilovers not installed.  If the tires don't rub, there is no metal to metal, and the lowest parts of my chassis clear the ground, I will check the coilover mounting length to see if there is a safety margin for preventing spring coil bind.

I read somewhere that you should design your suspension spring rate to take a 1g load before hitting the stops.  The bump stop load would be over and above that, so that's one hellova bump we're talking about.