Re: If it's not luffing, it's helping?
Not sure about the above. Because of the motoring the apparent wind moves forward and increases. As a result one might sail as if in 10 knots v 6 say at 4
instead of 2. The drive the sail produces depends on the angle to the apparent wind, and therefore requires the true wind to be somewhat further abeam. It may be that at 30 apparent you get drive whereas at 10 you get less drive than drag. In practice if you are getting more speed than the revs of the motor would give some of the force is coming from the sail as a result of the apparent wind increasing. Often the revs may be as low as 1000. However you still require an apparent wind angle which produces a force with a forward component. This may be say 30 meaning the twa is greater.
If the wind is in fact dead ahead not just light having the motor on will increase its strength but not produce a force on the sail other than drag think flags. Holding the boom to windward would produce a backward force.