Try using them on elements.
Ex. Find an earth element, use slowga. Then find a water element and use slowga.
If slowga lands on earth but not water, its probably water based.
If slowga doesn't land on earth but does on water, then its probably still earth based.
I've actually slept Tiamat with Shiva's Sleepga. Ice on Fire mob usually do not work that great. At least my 75 BP is resisted into 30ish damage. (and it should do 1111 unresisted)
But it may be just as someone said. Mobs in general being made to resist "sleep" or not, and it wouldn't matter if sleep was light based, it would still be considered the spell sleep and be resisted.