Koma is exactly right and yes the opposite is true for max power - theoretically.
BUT
I tried playing round with the knots on my REVs (13 & 9) and found no workable advantage at all.
IMO the range is so big on the latest SLE's that knot adjustment has become a bit of a dinosaur feature.
At the top end you really want to be sure your kite is going to perform when you need it too - surprises can be very 'not nice' when its nuking and too much depowering is likely to produce surprises.

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Trying to get more bottom end out of your REV by shortening the back lines is also counter-productive. Standard SS tuning on same knots has screwed every bit out of the bottom end for you already. More front line just makes them slower & less pleasant to fly. In fact on my 13M I never set my trim strap fully out - even in the lightest winds. I find it needs a bit of extra trim to behave itself acceptably especially when winds are getting marginal.