Live in SAN trying to go to LAS 2 days in a row.
There is a UA fare leaving SAN Monday morning coming back Tues evening for $140
Then there is a US fare leaving LAS Monday evenng coming back Tues morning.

I know that usually back-to-back would mean that you are doing 2 tickets but use different legs of those tickets for different returns. Since they are two separate carriers though... Idk. What say you?
The only reason I even care is that they will see it cuz of the miles.