Ref positioning prior to snap.

[Fiji07]

I've been taught to position myself as the R between 12-15 yds from the line of scrimmage and even with the tackle on the throwing arm side of the qb.

Our state observers have been observing games so far this and just recently published a list of the most common things they saw, both good and bad. The one that caught my attention was that the Referee was positioned to deep. I thought I would look at the Official's Manual to see what it said and can't seem to find anything about the position once the team has setup in formation. The only thing I saw was the position R should be in when the ready for play is blown.

Can anyone point me to someplace that specifies what that position should be by the mechanics manual or rule book?