iPhone 5/6 and 6Plus

Hey guys, I've searched for days and can't seem to find a solution I like. I'm trying to make an interface. I want the buttons to be the same physical size on an iPhone 6 as they would be on an iPhone5 - the only difference between the two platforms should be screen space. It seems that using the Canvas Scaler with "Constant Physical Size" would be the way to go, but that breaks down when viewing on an Iphone6+ because NOW I need the canvas to scale up. Constant physical size will no longer work as it will make buttons/text/etc appear too small on the 6+.

So how do I set it up so that when viewing on iPhone5 the game looks perfectly correct in all situations? I'm pulling my hair out trying to figure it out.