The difference is in the relative phase of the inner ring teeth with respect to the big ring teeth and any shifting enhancements the big ring might have such as shaped teeth, lift pins, ramps, etc..

For example, when shifting to the big ring in a given position of crank rotation, the the links may line up properly with the teeth on the big ring. At a different position of rotation, the pins rather that the links will line up with the teeth of the big ring and the chain will ride on top of the teeth instead of in them. One way ramps and pins improve shifting is by lifting and aligning the chain to minimize this happening.