You just need to experiment and find what works best for you. I have seen some people do better with 2 steps while other people prefer just 1 solid step. It is a technique with so many fine points to consider and just takes a lot of practice to reach your full potential.
yes I do brush my back against the tape in the video clips. but only because i am pushing myself to get through as small of a space as I can. also, when doing underbars outside, its not the end of the world if you hit the object a tiny bit. your momentum will carry you through regardless.
This month is a handy little drill for underbars. I taught myself really slick underbars using this method and still practice this every once in a while. It is such an easy drill to do and will have you doing tight underbars in no time. So go try it out and be sure to leave a comment here about how it went.