More often than not, the key to the pop transition is jumping straight up.  You need to get your center of balance above your feet before you begin jumping, or a degree of upward force will be lost, and often times your balance will be compromised.  As with most transitions, to slow down the transition, increasing control, a bit of under rotation before landing on the first leg can buy a little extra time for the second leg, and the rest of the body to catch up and align itself in the optimal position.