They are designed to float, although the header is much heavier than your sickle mower. There are two shoes on the back side under the header, which I suppose you could let it ride on them. I prefer to just nudge it up off of them, to keep from leaving gouges. Been meaning to get one of those depth collars to put on the cylinder myself, just never seem to remember to get one.
My hayfield isn't perfectly flat, but no sudden high spots. The only time I've had it scalp, is when I find a mound of dirt from a new groundhog hole.
Once you use a haybine, you'll not go back to the cutter bar. That reel is great for pulling hay in across the cutter bar, when it's a little tall, or you are mowing in the direction of a strong breeze, half blown over hay, etc. The only thing better in my mind, would be a discbine. I can't justify one of those for the small patch I make.
But hang on to your sickle mower, in case of breakdown, LOL... Been there, done that... I keep my sickle bar around to clip pasture, and to barber up around the hayfield.