I travel SYD-CDG-SYD via the USA about twice a year in coach, but I usually cannot predict my travel dates far enough in advance to always buy in France.

On UA Oz website, SYD-CDG-SYD costs about AUD 3,100 for outbound 1 Nov, return 15 Nov (example dates only).

On UA France website, CDG-SYD-CDG costs about EUR 1,500 for the same dates in the other direction. This is about 30% cheaper. It is always like this.

Similar results for other UA Europe destinations.

Any suggestions?