There was another video which showed how to calculate all the proportions (for a standard sized person, that is), but that seemed a bit overloaded to me - too many things to think about, rather than the essentials and then let your mind (and hands) go free.
I keep having a picture in my head of the slipstitch patterns you were using for the hat for your sister - I'd like to adapt some of those. I specially liked the grey/white/black colour scheme.