Re: showing my newbie stripes but...
BG smalls aren't super absorbent, IMO, but worked great for us since I didn't have very heavy wetters in the beginning. Both of mine outgrew the absorbency in smalls before they outgrew the actual size of the diaper.
As far as the rise goes, it has a bit to do with the legs--try it out, if you unsnap it all the way, it makes the legs huge. If the legs are too big, you'll get leaks at the legs. If the legs are too tight, the diaper will leave red marks. The weight ranges are only guidelines; some babies can be very short and heavy (and have big thighs) and need to be on the medium or large size, and then when they get taller and thin out from crawling they go back down a size (even though they weigh more, their legs are smaller).