What I've been trying is exposing for the background and then generally using the softbox at a 45 degree angle and about a foot above subjects about 8 feet away.
Eight feet? With a softbox? And a hotshoe-sized flash?
Um...you do know that the whole point of softboxes is soft light, and that they really only can do that when they're right on top of the subject? Otherwise, simple geometry causes them to turn into small lit sources, not significantly bigger than the pinpoint of the flash in the first place.
If you're not trying to figure out how to keep the softbox out of the shot, you might as well be using a smaller modifier (if any).
I could maybe see a softbox eight feet away with a monster-sized softbox and a group shot, but I don't think you're going to be lighting up something like that with a hotshoe flash.