quick update - found the root cause...
I was looking at the wrong radius server's logs...
Apparently because I also have a valid user certificate for the same CA on these iOS devices, they'll use that to successfully authenticate against my Freeradius3 install through eap-tls rather than user/pass. Going to have to make some chances there...
I'm still surprised that I never get prompted for a user/pass either when the profile is installed or it tries to authenticate the first time through EAP-RADIUS