Let up on the forward movement button / stick direction if it looks like you are going to overshoot, or try jumping from further back on the starting platform. Depending on the situation using a high camera angle may help; others have found it easier to jump with an over-the-shoulder view (hold the left trigger down for the Xbox version, or use a close camera view on the PC).
There are 3 teleporters in that cave (one teleporter up high, one mid level and one on the ground at the bottom of the cave). Only 2 have generators, but you still need to do all 3 before taking out Barnabus, or the last room in one will remain locked.
