Have you seen the adjustable jib cars that Brett has fitted to his boat? I think Mark and Tony have the same…(If you double click the photo, it should enlarge…)
A bit fireball-esque, and unlike conventional FF jibcars, these adjust vertically. You will note they also have lateral adjustment of a couple of inches. The red adjustment line gives the vertical slot control.
The other thing that will strike you, probably, is that they look a bit lethal!! However, the clever answer again is that they are sprung loaded vertically, so hopefully pretty kind to the crew leg….
We were wondering if this is the way the new rig will cause jib cars to go in future??
The Flying Fifteen Blog 
How many of us are skilled enough to alter our jib leech in two directions?!!!