I think you've got it !! After reading some of the links to previous answers to this question, I like your theory the best. C&H says that their system doesn't measure RPM but the dwell angle timing (time that the magnetic switch is closed) to determine firing delay. There are a few variables here, the width of the magnet and pickup, and how far out from the centerline of the prop shaft (radius) that the magnet and sensor are mounted. Both of these would influence the dwell time. I assume that both of these factors have to be within certain limits. This explains how Syncro Spark knows to delay spark at low RPM on the very first flip. When setting up the initial timing, even though the system is saying to delay firing to zero degrees when you are slowly revolving the prop shaft, the delay time is irelavant because you are moving the prop hub so slowly. When you are flipping the prop to start (600 RPM or so), the delay starts to become relavant. This makes sense to me. Thanks