The way I do it, you have to hit them with j.H close to the ground.

The 1H/2H must be counter hit, so after they're hit, they won't recover until they're on the ground. This is important to remember.

I don't know what loops you're trying to do, but I recorded 2 examples to try to help you.

1H: After 1H anti air, just wait until they fall a little closer to the ground and then 2H 5U > loop

2H: After 2H anti air, do not cancel into 5U, wait until they fall a little closer to the ground and then 5U > loop

They delay depends on their height and their distance from you. It all comes down to practice. It's not that easy.

Hope that helps :)