On a lot of these 'up-in-the-air' moves, I can't do everything at the same time. If I jump high (well, high for me!), I can't get my heels together. If I jump wide, I can't get high.
For plié jacks, I can sometimes get the heels together, but I put more emphasis on the downward portion of it than on the upward.
But don't worry, you don't have to do plyos exactly as Cathe and the crew do for them to be effective for you. In fact, IMO, if you try to force yourself into a move and your body isn't built for it, you could do yourself harm, not to mention get frustrated as all get-out!
Just look at some of the background exercisers, they don't always do a heel click. (Though it does seem like Cathe has weeded out her background exercisers and just kept those who can, LOL!) It does seem like taller people can have a harder time with some of these air moves. And I don't mean "tall," just taller than Cathe and the other short backgrounders, who are around 5' 2". For example, in earlier workouts, Rhonda, who is 5' 6", did not get many heel clicks in. I wish she were in workouts still, because she's my height, and its nice to see how moves work on taller folks.
Just work it, do your best, and don't worry about the details!