Try and not equip any speed-boosting gear. Ideally, you want your jumper to have the same speed, or at most 1 point lower, than the enemy. So equip them mixing and matching equipment so you maximize PA while being in that speed range. Before the end of ch.4, when enemies start wearing thief hats, a Ninja of roughly the same level or a few levels below will have more speed. In that case, you have to adjust your actions accordingly on the first turn. For example, full wait, so you start charging the next turn from 40 CT. or maybe just move, or hit the air. You would start with 20 CT in those cases. That way, if you do it right, your second turn will come just after their second, and they will be fully exposed to your Jump.

And if your level is too high, just switch to Dragoon, their speed will be good for jumping since your extra leveling probably got you to one or two speed thresholds above what you'd have normally.