Nedra taught this in class a few weeks back:
.#1 Front Crosses make D speed up.
With a slower D, do a FC wherever possible.
#2 Rear Crosses make D slow down. With a fast D, do a RC wherever possible.
This one stands to reason, as D wants to stay with H and a RC slows down H's forward motion, pulls D back.
With slower D's, RC's work pretty good on contact obstacles where D's speed is slowed down anyway, and when D is in midair over a jump, maybe not so good on the ground.
A RC is hard to perform very close to the jump. It tends to push D sideways and away from the jump. Here's a video clip showing what can happen.
You have to time your RC so it occurs just after the previous jump. This means you have to send D straignt ahead while you slow down and cross diagonally behind them, without slowing D down. This is difficult, as D is generally trying to stay with you and match your speed. Need lots of SEND practice and ARM CHANGE practice to do this well.