50k port range

our set up is SFB 2015 Standard Edition with 2 pools (each with its own Edge server)

publicly our AV Edge servers are only open on UDP 3478 and TCP 443 and the 50k port ranges are blocked.

in the past when a remote user on one pool is remote and wants to call a user on the other pool, the snooper logs show the media going between the 2 AV Edge servers.  I understood this to be the correct behaviour as the 50k port were blocked (albeit not the most optimal).  so it mirrors the example below where the 50k port range is closed

 50K port range example

Recently i've noticed that when remote users on one pool call a user on the other pool, the media path is between their server reflexive address and the public IP of the callee's AV Edge server. 

I realise this is more optimal as only one AV Edge is involved it the call but i'm trying to understand how it is working when the 50k port range is being blocked.  i'm assuming there's some clever stuff going on in the background where its using a recipricol connection?