Over the years all the bases on the four corners of the country have always been the most senior. BOS, MIA, SEA and LAX being the four corners. I was a 757 F/O in BOS when they closed it in 1996. A month or so before they closed it, we were sharing a motel van with an ATL L10-11 crew to the layover in NYC. They asked where we were based, we told them. Their Capt. asked, "So, where are you going to go when they close it?"
My Capt. said, "L15 in ATL." I said, "MD11 F/O, ATL". Their eyes got big and the F/O says, "You guys think you can hold that?"
I just laughed and said, "Well, he's number 350, and I'll be half way up regular lines on the MD11."
BOS was always senior, many guys retired off the 727 there rather than commute to ATL for the L15.
And that's also why LBP will make the smaller bases more senior, nobody will have to commute to ATL for a pay raise. Guys will be retiring off the 737 in LAX at top pay.