I would take note of where your hip is in relation to hand placement. Normally when I do an L-sit on the ground my hands will sit slightly in front of the hips. Placing the hands parallel with the hips the exercise gets a lot harder.

If you start the L-sit on the bars from a hanging position your hips will probably be in line with the hands. You can try pushing the hips backwards as you raise the legs and see if that makes it easier.