In order for a person to step on top of a step, there must be a step to step on!
The feel of a vocal step corresponds to vocal cord adjustment. When the cords are drawn into the exact length, width, and depth by the closer and stretcher muscles for a particular pitch, the singer has the feel of standing on the step. As the other vocal adjustments are correct, then we feel like we step up and step down, never attempting to approach the step from underneath. Imagine trying to do that with a ladder, we won’t get very far.
We always step on top of the step. As the adjustments become more and more correct, then we will find that it all happens more and more automatically. We will have a particular feel and mental concept that will accompany this happening. Then, it is a matter of repeating and remembering until all this top of the step activity becomes second nature!