I will often use market fares because I don't have IKK, and let's face it, unless you do it's rare you get a decent routing, unless you've got time and want to set up an ExpertFlyer search and wait.

I'm curious what determines "market fare". Usually, if I find a lower fare on aircanada.com, Aeroplan miles match appropriately. But sometimes, it doesn't.

For example, I was trying to book YYC-PHX, and some very inexpensive Tango fares booked into fare class K, but Aeroplan had a 35,000 mile trip booking into A (which I think is Flex). Are there rules on which fare classes Aeroplan can book into, even if it's for sale on aircanada.com?