IPhone : AutoLayout Size Classes - different proportional heights

I need to set the height of a subview to be proportional to its parent. On iPads, I need it to be one third of the height while on iPhones I need it to be one half. In the "AnyAny" size class, I create the constraint and set the multiplier to 0.3333333. This does what it should on iPads. When I change the size class to "CompactRegular", I change the multiplier of the constraint to 0.5. Although this makes it half on iPhones, it also does it for iPads. How do I make it such that the size classes would have different multipliers?