Hi,
I suspect that it's either retensioning the Top (adjusting the Tension Cable Ball Joints) or that it may not be timed exactly side-to-side (adjustable in ¼ turn increments of the Top Cables at the motor).
But, I really can't say because I've never driven my Boxster with the Top UP, not even one time. Guess someday I should at least try it once, just to say I've done it...
Happy Motoring!... Jim'99