That is stacks is indeed an easy to miss advantage of this wonderful spell. I don't think there is a 'stacks 3 times' limit; rather, given the short duration of the spell that is about all you can get off before the first one expires. I just tried laying down a row of them and could get between 3 and 4 on the ground at the same time. I know rippling a couple on allies in trouble works well and often saves me from using my more expensive Breath of Life.