What I did for many years was a sort of Papazian old-style method, where I'd actually put the grain bag into a colander, heat up some water on the side to 170 F, then very slowly pour the water over the top of the bag in the colander. It's very time consuming, and basically constitutes a sort of fly sparge but without the sparge arm. Kind of a pain, but it will get the efficiency way up even into the 90s.
This is what I do, but I don't get efficiency in the 90s. How much rinse/sparge water have you used?