When you go to kick in again, your boot will not get all the way in. It will be resting on the highback. That is correct. From this position, pull up on the high back, and stand down on your heel. The boot will "shoehorn" into place. As your boot will always be moist from snow when riding, this is very easy when riding, a bit harder when dry.
The issue that I think beginners (or simply Flow novices) may have with entry is that the standard technique, which you have described, can be problematic on nonlevel ground. It's easy enough to put in the front foot down at the base of the hill, when you can anchor the board with the other foot. But kicking in the back foot will have to be done on unpredictable ground at the top of the hill, or perhaps in the middle of a slope if you had to stop and skate for some reason. Once you put your back foot into the binding, your anchor is gone and the board can start to slide downhill, perhaps rapidly. A beginner, or someone who's used to putting on strap bindings by sitting down, may find the "kick in on the fly" experience unnerving. The kneeling technique I suggested is the Flow equivalent of sitting down: you can do it on any slope, you don't need to dig a ditch, and you don't slide while doing it.