Actually I see that I could get back to NYC for, in theory, 19,853 miles. But that's assuming AA matches the Great Circle Mapper. on my routing (also assuming BKK-HKG-NRT-NYC). If I just do HKG-NYC its 19,341 miles. Better, but still really close to the 20K limit. I could do Iberia BOS-MAD and lower these numbers to 19,668 or 19,156 respectively.
Ideas as to how close I can expect AA to be to these numbers?