What's the difference between MAC's Studio Fix powder and Studio Tech powder foundation?

Studio Tech is a cream to powder foundation with more coverage than Studio Fix but not as much as MAC Full Coverage Foundation. Studio Fix is just a powder foundation with medium coverage. Personally I use all three...I use the Full Coverage with the Studio fix on top for really special nights when I want that ';porcelain doll'; look, Studio Tech when I don't need as much coverage, and Studio Fix for everyday...