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If the wipers sit below the 'hoodline' as you call it, then they'd be in, or very close to, a vortex created by the transition from hood to glass. If they're inside, they should have no effect, if it's outside, the effect is there, but is so minimal as to make no difference.
I've only done a bit of fluid mechanics, so don't take my word as true, but that's my take on it.
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