Inbound fax call not being detected as a fax

When a voice call comes into my system, it rings 3 extensions because they are in the Ring Group.

Now, I have an iaxmodem on a new extension 56432 and I can see it registering and renewing regularly.

Accordingly I did these settings in freePBX

-> General Settings -> Fax Machine -> Extension of fax machine for receiving faxes: IAXmodem1 <56432>

and in

-> Inbound Routes -> Route:/4444/ -> Fax Handling
-------------------------------------> Fax Extension: IAXmodem1 <56432>
-------------------------------------> Fax Email:
-------------------------------------> Fax Detection Type: NVFax
-------------------------------------> Pause after answer: 3

But the inbound fax call is not being sent to extension 56432.
Instead the 3 extensions in the Ring Group still ring as they use to.
When I pick up the phone on any of the 3 extensions, I can hear the fax tones.

So, why isn’t NVFax detecting the fax tones ?
Is that the reason why the fax call isn’t going to extension 56432 ?