Ah, you’re referring to my question and the subsequent answer from SRAM that I relayed in the Favorite flat mount dropouts thread.
I have a feeling that the spec in the SRAM and Shimano docs is supposed to be universal and it does not differentiate between materials. I can certainly see how a carbon fibre or aluminium boss that’s thinner than 10mm could pose a problem for yield strength or flex. Steel and Ti though… probably not as much.