When it comes to recapturing our flag, It doesn't matter where you fight really, as long as it's where the flag is, and normally it becomes visible on the map when they're somewhere in mid.
However, the sides of the BG's middle are more valuable than the actual middle. People in the actual middle are usually just HK farming (Which I've been doing more and more latelly because I sometimes can't be bothered anymore).
It's very situational, just like everything else in pvp, it does matter where you fight(such as killing EFC), many times you need to make a decision real quick whether you should keep stealthing(since you're a rogue) til the EFC gets to the flag room(i'm talking about both team have flags now) or you gank him in the mid field, and the decision can be made based on things such as whether or not the EFC has a healer following him, how many heals following him in total? where's the majority of your team? are they all died in GY or are they near you and planning on doing killing the EFC in mid, you want to join the fight when the majority has set for the fight, and observe the situation, if the fight went bad you need to save your vannish CD and go follow the EFC and his healer until he got to the flag room, many times the opposite team will choose to kill FC if they won face-face fight, and that's when you as a rogue go kill the EFC while everybody else not around.