Codec Selection Order in Asterisk SIP/IAX Settings

Does anyone know the codec selection order if I use the ‘Asterisk IAX Settings’ module? There are check boxes for selecting the required codecs but nothing to specify the order in which they are tried/used.

In IAX Settings I have selected alaw, gsm, g729 & ilbc and they appear in iax_general_additional.conf in that order.
I want the selection order to be g729, gsm, ilbc then alaw and I had them in that order in iax_general_custom.conf.