Think of the half axel in two halves. First get the kite into a flare: a bit of slack on the top wing and then a harder input to get into a flare. Then a softer input on what was the old bottom wing to lift it out of the flare and then pull on both lines to power it away.
If you think of it this way, the transition to HA cascades is much easier.
You can also break the trick into two parts. Practice the flare bit first and then when you have got that, you can move onto the second half lifting it out of the flare and powering it off.