Reserve is a function of seniority. Horizon has a large number of very senior pilots who aren't going anywhere. This means we're pretty stagnant anywhere except for the bottom of the seniority list. Like I said, just a few seniority numbers means a lot at this company. The guy just above me has been able to hold a line for a year now. I have not.
Your base changes only under special circumstances.
1) You voluntarily bid to a different base. Moves are awarded in seniority order, and only when there is a vacancy to fill. You can be the most senior guy in the world, but if there's no vacancy, you're not going anywhere.
2) The company opens a new base, and no one wants to go there. This would result in a displacement for some junior people.
3) The company closes a base, which would displace all of those people to the other places, in seniority order.