Copy Value From Cell in Column A to Column B And Vice Versa

I don't know how to exactly describe the Problem with words. I hope it is self-explanatory what the UI does. I can think of two variants of the Copy-Arrows.

I am looking for User-Studies or at least heuristics on which variant might be easier to understand. I'd also be happy to know some key-words I might use to find results online.

Variant A: Arrows Point to the middle

Variant B: Arrows Point to the outside