IAX trunk codec order

When I select more than one preferred codec in “Asterisk IAX settings” , I noted by “iax2 show channels” command , the working codec is always the lowest among selected ones in the list.
Is this correct ??
(I suspect is the same for SIP codecs)

Both the SIP stack and the IAX2 stack will negotiate and accept the first mutually acceptable codec. The order of “the list” is up to you.