FRL evaluation between SM and CM

[jlapine]

It seems that everything I thought I knew about COR's and FRL's is wrong!

Here's my setup:
I'm installing a new Aura solution comprised of CM with ISDN trunking for local and LD calls. I have a pair of Session Managers connected to CM via SIP trunk. SM is supporting a third-party iPhone based SIP application that requires access to off-net trunks via CM.
SIP endpoint FRL = 5
SM-to-CM trunk FRL = 2
CM ISDN PSTN trunk FRL = 3
Route Pattern FRL for LD calls = 3

Here's my confusion:
Local calls from SIP endpoints completed as expected. LD calls from the same devices received a denial indicating they were blocked due to inadequate FRL (denial event 1343 in CM list trace and traceSM). After much head-scratching I changed the FRL of the SM-to-CM trunk from 2 to 3 and placed a successful LD call.

Here are my two questions:
1. Why does CM seem to evaluate the FRL of the SM-to-CM trunk when making PSTN routing decisions instead of the FRL of the endpoint?
2. How do I restrict SIP endpoints if the FRL of the endpoint COR is irrelevant in PSTN routing decisions?

Thanks in advance for the input and ideas.