The bold above may be your problem in harnessing it. That may be consistent with how you perceive Macci, but I think you hit the nail on the head about what he and Gordon have not realized yet. They think the flip creates SSC that is immediately converted to power for the stroke, but the flip and drag only load the system so that it is ready when the power action takes place.
The lag is started with the flip for the atp and the flip is important to power later in the stroke....but not via a snap at that point. The flip sets the racket into the lag position to drag the racket with the head loaded with feel and force. Using this drag, you pull the butt cap to near the contact. At that point, the hand changes directions to pull more across the body, tightening the arc as it starts on what will be seen as part of the follow thru. The racket head, lagging the actions of the hand, will be powered to continue out to contact much like someone riding an innertube behind a turning boat. Just like the boat driver can control the tube riders pace and power, the hand can feel and control the racket head as it powers out to and across contact under acceleration. Make sense?