I've been watching this topic with interest as my yb's have only been flying for about twenty minutes or so then coming down again as well.
Yesterday , rightly or wrongly i decided to bite the bullet and took then approx 7 miles for their first training toss...got them all back in one batch after about 15 or 20 minutes no problem, i let them out an hour ago this afternoon and they are still up and bombing about, that toss has hopefully brought them on that little bit and will get them ranging all the more.