Why would diclofenac have a higher skin permeability when formulated as diclofenac epolamine rather than diclofenac sodium?
Voltaren is a 1 -2% paste of the ammonium salt of diclofenac (epolamine is hydroxyethyl pyrrolidine) and is used a topical pain reliever. You can smell the ammonia.

It could be that the increased pH of the paste softens skin and makes it more permeable. High pH will peel your skin right off!