Some of UA's awards are not as generous as AC's...

The way AC and UA classify zones is different and that makes a big difference in some awards.

For example, Hong Kong to Tokyo is 40/60/80 on UA's chart yet it's 20/30/50 on AC's chart. Of course, this might be done intentionally to encourage people to fly on UA metal between SIN/BKK/HKG & NRT so UA don't have to pay the *A partner back.

But in general, UA's chart is more generous for long haul flights.