It is known that nat= is only needed for cases where the peer is inside and Asterisk outside, but my comment was only just as an aside about a deprecated option, in case he need it on the future, but thanks for adding extra information about the correct use of nat
It’s not generally known that that is the case. My impression is that most people use it because they are inside NAT and see this nat= parameter and assume they have to set it (unfortunately, they often assume it is the only thing to set).