Last year I began using Russian grips. I almost always do it successfuly standing upright against a bent over opponent. In fact, that's usuallt when I go for it the most now. Russian grip Uchi-Mata is a great solution (for me at least) to someone who is bent over with their weight back, and legs spread.
I have to agree that Uchimata is the perfect throw from this position. Especially since you only need to commit one leg, and have a ton of power from the grip on the belt.