Garage exposed NM wiring - protection?

I have built a steel garage kit. All my horizontal NM runs are 9 1/2 feet high, fully secured (with closer spacing than code requires), and where needed I added pieces of steel studs to provide secure attachment and protection. Of 550 feet of NM cabling there is literally just a few inches that are not immediately adjacent to a piece of steel. The problem is the nebulous wording of NFPA 70 334.15(B) "Cable shall be protected from physical damage where necessary….."

In various posts/articles across the web (including this forum) people make statements similar to "wiring over 8 feet is considered protected" yet I can find no explicit statement in the code nor does any writer quote a reference to any such rule. Is there any such code/rule? My inspector says I have to construct coverings over all my horizontal runs – wood or plywood or drywall – to give them ‘protection’. Almost 10 feet up in the air. Clearly absurd but I am not sure what the rational rebuttal is. Any suggestions would be appreciated.

Update: should have mentioned, state is CA. I found a document that seems to list all CA modifications to NEC, scanned that but did not see anything relevant. The primary special feature was that I ran oversized conduit to the subpanel and left 2 breaker positions open, so someone someday can pull a bigger feed for a car charger. They like that kind of stuff out here.

Success!! Inspector came today but was not the previous one who is still (I think) officially assigned my permit. Anyway, I had articles printed out as mentioned below, we had an intelligent discussion (which did not seem possible with the other one). Contractors typically put up (unpainted) drywall in garages around here so possibly these guys do not deal with exposed NM much, who can say. But he agreed no mechanical protection needed for NM over 8 ft in the air. Whoopee! Thanks for the extra code reference, I figured the 8 ft number was coming from somewhere.