It has long been a general rule but there there references peppering aa.com. Here's one:
How will my award miles and EQDs be calculated if my ticket includes both American marketed and partner marketed flights?
For tickets including both American marketed and partner marketed flights, award miles and EQDs will be calculated based on the policy for each flight – American marketed flights will earn based on your prorated ticket price (base fare plus any carrier-imposed surcharges); partner airline marketed flights will earn based on a percentage of the distance flown as determined by the fare class purchased.