Vertical is vertical, whatever your grip type; either the wrist is or isn't. I don't think that "vertical" is relative. If you play with a 90* turned left hand grip at impact, then it won't be vertical to the ground until very well after impact, unless you're happy with going left of left.
Another way to look at it....
The farther 'up plane' your impact, the more the left wrist is in a 'turned' position. Part of the reason that the back of the left hand should match the angle of approach, not face the target. All of course subject to the rest of the machines alignments and the intended result.
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