IMO the only way to see how it affects to the club face is that we put the club head to the same place and see what happens it if the wrist is cupped or bowed. That way we see how it changes relative to the path or plane. That way at impact the bowed wrist will produce more closed club face than cupped wrist and that's the only thing IMO that matters. Moving it away from that point for sure opens or closes it relative to the target line, but not if you bring it back to that place without changing the wrist orientation.
The bowed wrist will bring the face to impact later than cupped wrist, it's clear, so the hands are more ahead and it's anyway made by twisting the shaft in that relation.
So by bending the left wrist it can be more closed to the target line, but also the whole geometry is changed and hands are more behind the ball. Also the bowed wrist can make it more closed than cupped when you change the hand position in that geometry. But basically the bowed wrist will create more closed club face if everything else stands unchanged.
