Jetty-syns don't have very complicated AI, and henceforth they're rather easily faked if you figure out what they try to do. Jetty-syns attempt to stay about 100 fracunits above your player at all times. This of course means that they'll hover at jump height when you're on the ground...however, when you jump, they'll try to stay 100 units above you and dodge your jump by flying up. However, they don't do it as fast as you do, so if you jump to fake them out, land, and then jump again, you can catch them on the downward movement and they die easily.
Once you get the pattern down, it's easy to slaughter them like nobody's business, especially if you only have to deal with 2-3 at a time so you can keep them in view. The problem comes when there are enough that a gunner can get behind you can shoot you in the back ^_~