I've always found 6-4-2a and 6-4-5a to be a contradiction. 6-4-2a states that a non-jumper cannot enter the center circle until the ball is tossed. But 6-4-5a states that non-jumpers can't break the plane of the center circle with his/her foot until the toss is touched by one or both jumpers.
So, does that mean that the non-jumpers can enter the circle after the toss and before it's touched as long as they enter head and hands first?
It would seem that if 6-4-5a is the requirement, then 6-4-2a doesn't even need to be in the book.