Actually, having read the manual, you pop in a slide holder, spend 20 minutes scanning it at various heights, determine which one is most appropriate for your hardware, and forget about it.
Unless you put in an absurdly warped negative, in which case it probably just doesn't matter.
This is an automated version of the process I went through with my v800, and strangely, I've only had to do it once.
We're both speculating on a process neither of us has experienced, but at least I'm willing to let the film take care of the negativity.