I tried an experiment this year with the hyacinth in that SUPPOSEDLY, they like to be confined.
That does seem to be part of the formula. However I find that mine will bloom if the roots can reach the "bottom" - so they like being in the pondless waterfall that's very shallow. This year I tossed some where they couldn't float away in a spot between some rocks - they loved it there, got really lush and green, and that's the one that bloomed. So that will be my strategy next year - find spots where they can almost become marginals. I just love the blooms - they're so pretty!