Dickita and D.D. bring up a good question and I honestly don't know the answer. It could go ether way, I think, depending on who is doing tech on a given day.

It's analogous to the cage rules interpretation that requires non-required bars (oxymoron there) in a rollcage to meet the minimum size. I can have air in the diagonal across the roof, or the minimum-size tube, but nothing in between?

Or those damned fire systems again...

K