Can Self Leveling Compound be Poured Over 2 Inches Thick?
If I understand your question you are creating a raised floor section, 2 1/4 inches higher than the floor below it and you want to place you tub at this height.

I think that you have some sort of frame in place into which you want to pour the LevelQuik, filling it up, so that it will cure into a level surface.

I suggest against that. The maximum thickness of the LevelQuik is stated because, among other reasons, it may not cure properly when poured too thick and it may lose structural integrity when poured too thick.

I'd suggest you use a Deck Mud mix and scree it to your level. If you're nervous about the trueness of the level you could pour the Deck Mud slightly below your line than pour LevelQuik on top of it.