How do I provision an IAXy to use a non-4569 port?

For IAX connections, I wanted my asterisk system to use port 21821 (instead of the default 4569) on the server side.

So in “iax.conf”, I made the change “bindport = 21821”

After restarts and all that, it works.
So on the asterisk server side, all IAX2 connections are handled on port 21821.
Great! This is what I wanted.

Now I need to send an IAXy ATA to a remote location.
The IAXy device CANNOT use port 4569 on its end either.

I want the IAXy to use port 31431 for itself.

When I initially provision the IAXy -
In the “/usr/src/iaxyprov/trunk/iaxy.conf” file, I can only specify the ip and port for the server:
server: <server1.ip.address>:21821
altserver: <server2.ip.address>:21821

Alright. The server is taken care of.
But how do I provision the IAXy device to use 31431 for itself (instead of the default 4569) ?

Thank you.