Is there any reason for preferring two segments per side over one? Is there any reason not to use say a single 6" arm per side for macro and a single 12" per side for wide angle?
The setup I just used for macro was, on each side, Ikelite handle to ball adapter, clamp, 5" ULCS double-ball, clamp, short Sea & Sea ball adapter. I found that with the extension and flexibility of a clamp on either end, and the inches of the ball adaptor, that a single arm, even a short one, was fine for macro (90mm). I liked the results I got with the strobes usually pointed in, and didn't find a need to elevate them much, if at all, over the port, so the short arms were not a problem for me. I thought this gave pretty even and shadowless lighting, which I liked. (And it kept the whole rig fairly tight and easy to use, which was a big plus, as it was my first time using a DSLR underwater, and first time with 2 strobes.) Maybe this one would have been better with a little more light from above, but you sure get a good look in the mouth.
I think that for macro, setting up the lights with single short arms, on about the same horizontal plane as the lens, helps get into narrow spots like this one. The crab was tucked into a narrow crevice:
I guess I'd do something similar next time, but will probably take 8" arms too, and add them when shooting wider than 90mm.