Who says they can't maneuver? They didn't in the trench because there was no room. But as long as they were pointing at the port, there's no reason they couldn't jink back and forth or even corkscrew around the cone and still keep pointing the TC at the port.
Really? Because none of the targeting computers in any of the games work that way. The moment you move your reticle off of your target, you lose your target lock. So no, generally speaking, you CAN'T jink back and forth or corkscrew and maintain your lock, unless your target is also doing those things and you're doing it to keep them lined up in your sights. Which an exhaust port is obviously not doing.