Welcome to the Gulf Stream Owners RV Forum!!
Congratulations on your purchase of your Prairie Schooner.
From your description it sounds like your slide/patio awning is just like our kitchen slide with the patio awning right over the slide. I believe you are correct in that the slide must be in to extend the awning, just as it has to be for our MH.
I extend the awning then raise it, yes very high, then move the slide out.
I keep the awning just high enough so that it does not touch the top of the frame of the slide. After you do this a couple of times, you will know how far up the awning must be raised for the slide clearance. (HINT: Mark the hole in the awning arm were the handle lock pin goes thru so that you will know in the future, I used permanent marker to do this.)
I always use tie down straps that go around the awning roller down to screw in anchors just as a precaution against the wind blowing the awning up since it has to raised so high.
Enjoy, Ron