I must be missing something. I'm looking at current versions of 2.6A and 2.4C. Both state (III,1,a) that "The entire roll cage shall be constructed of 1 1/2'' x .065" tubing with a minimum of five (5) points of attachment to the shoulder hoop(s)."
The only reference I find (both specs, III,1,g) to an 1-5/8" requirement is when roll cage height from shoulder hoop centerline to the roll cage hoop centerline exceeds 18", in which case 6 points AND 1-5/8" are required.
So I'm a bit confused, here...