Dr. Sane,
I shoulda' mentioned that I like to see the barrel or barrels roughly parallel to the wall. But, if I don't get that, the 1 1/2 -2" figure works out OK, for me, anyway, regardless of gun type, or barrel length. From the shortest barrel here, to the longest is a difference of about 5".
The other guys need to find out what works for them.
We've agreed on a few other things over the years. Actually happens enough to cause me to wonder if I just might be legit.

Best,
Ted