Magic loop is on a video in the Advanced Techniques
section for small diameter knitting. You would use at least at 30" needle and yes, needle lengths are measured tip to tip. I do a variation that's kind of a half Magic Loop; I only pull out the cable on one side. You'll understand maybe after you see how to do the regular ML. The advantage is that you can use a shorter needle and you don't have to adjust your stitches quite so much. I use 24" ones for hats and they work out okay.