Ya but are they always those two locations or will it change based on who you side with
No.
Ulysses is (or was) a Frumentarii who fell in love with a nation the Courier helped build up, until it was tradgically destroyed by the Courier's own negligence. Since then, he's been unable to appreciate the Legion, the NCR or any other nations as he believes they're all doomed to fail and pale in comparison to what the Courier was building up. Ulysses believes that in order for another great nation to arise, all other "dead" ideals and nations built upon them must first die. However, he sympathizes with the Legion, their ideals and their decent attempt at trying something new, thus instead of bombing both, he opts to bomb the Long 15, cutting off the NCR, dooming their forces in the Mojave so that Vegas will fall to the Legion, then the Legion will have a CHANCE at building a strong nation, and should they fail, they'll surely turn on each other and then a new nation will be born. This plan remains static no matter which choice you make.