A great way to work the step-out is with a drill I have used for years. You will need a resi-mat, and an incline mat.
Put the incline mat on top of the resi so that the pointed end of the incline is pointing towards the center of the resi.
You will start on the incline doing a forward roll up the mat, so that when you would normally stand up, you would be falling off raised end of the incline. This will simulate the end of your punch front.
Practice rolling off of the mat and kicking open to step out into a round off. This will help you learn where in your punch front you will have to begin to open to be able to properly step out.
If you don't have the equipment, this drill can also be done with a trained tumbling instructor by having them lift you overhead in a tucked position, then lowering you while you step out into a round off.
Basically they would start with you being held in the "back tuck set drill", then have you roll forward and step out... This is a lot of work for the spotter and would recommend using equipment if you have it.
Hope this helps!
-Coach Matt