Thank you: while interested in general about this question, here is specific example: SNA-ORD-MIA. Depart at ORD, and reboard same plan about one hour later. One AA flight number. Posted only 2,331 miles.
Can you be more specific so we'll know what you're talking about? Your question/concern are not clear to me from what's written.
One question- was this multiple legs with the same flight number? More info is required.
Cheers.