The best snaps (either purposely or accidentally!) are when the wing stalls, and it sounds like your wing is flying you through the maneuver as opposed to the model tumbling through it.

Increasing the elevator throw should improve the snap (at least, that's the main cause of an unwanted snap!). You could also try slowing the plane down to nearer the stall speed before trying the snap.

Also, a CG set back helps, but might make the plane too sensitive for the rest of the flight.

Just my 2.6c !

-David C.