On VG224 , you can choose asymetric G711 codec with the voice service voip command for the fax issues.

voice service voip
!
modem passthrough nse codec g711alaw
!

The modem passthrough commands will determine the G711 mode used for outbound calls

But the following part of config will determine the codec use for inbound calls :

!
dial-peer voice 15 voip
description <=== avoid PVID 0 in VG224 ==>
answer-address .
modem passthrough nse codec g711ulaw
session target ipv4:<<loopback_address>>
!

So in our case , the incoming calls will considered in g711ulaw and outgoing calls will be treated as g711ulaw