I spent some time pouring over the APA contract, and one thing which jumped out at me (Under supplement "AA") is that they do talk quite a bit about Long Call/Short call. The general gist of it, is that crew scheduling looks at the next days requirements and assigns each reserve pilot either Long Call or a Short Call Reserve Availability Period.

While you can't "bid" for Long Call for the whole month, you can submit your "Preferences" for RAP or Long Call, and Crew Sched is supposed to take those into account in seniority order when they process the next day's reserve assignments. So a senior reservist should still be able to get Long Call if that's their preference. Theoretically. At least, this is my understanding after reading it.