With AA, IPC is considered in their South Pacific region, rather than South America 2 so it would be a higher award amount.

I don't know for sure, but wouldn't be surprised, if the IPC leg you're seeing on BA is phantom availability even if you get all the way to the payment page. The last time I considered an IPC trip using Avios, I would go all the way to entering my payment and clicking to complete the purchase on BA.com and only then did it come back with an error or unavailability.

I'm once again looking to include IPC on a trip and am planning to just pay cash for the SCL-IPC roundtrip.