From a personal experience, I have found that whey-based proteins, seem to be the most soluable, as opposed to soy and
casein (egg). The stuff I take now is a whey isolate/concetrate blend, and I can mix it with a spoon. Any powder with casein or soy protein- I've always had to mix in a blender. I'm assuming you mean 20 oz of water and not 2 oz?