Andy, I would approach pizzicato as needing a range of techniques to give you some control over speed, tone and projection. Others may disagree with the following.
Very broadly speaking, if you pull across the string and down onto the fingerboard with the side of your index finger about 6 inches from the end (jazz?) you will get a different result than if you release across and up with your fingertips closer to the middle of the string (harp/classical?).
The jazz one is perhaps at its best with your hand pointing down diagonally and your thumb on the side of the board to pull towards (but avoid the rosin). A classical pizz here gives you a stiff thump and not much tone, sustain or projection. Come a little higher towards the middle of the vibrating string and it becomes less stiff. You can turn your hand so that two fingers can pull across and down, using more weight of your arm to pump out a bigger, heavier sound. Or you can develop rapid pizz with two or three fingers, useful for jazz and classical.
"Classical" pizz IMO is best somewhere in the middle 1/3rd of the vibrating string length. You need to experiment with where to pluck, looking for the places that give the elasticity, sound and projection you want. This can change from note to note sometimes. Not only where but how you pluck is important. You can range from snapping your fingers off the string to rolling the tips off with no snap, just release. Whether you play German or French bow will make a difference. As a Frenchie I personally feel most comfortable with my hand higher than 1/2 the vibrating string, closer to my LH and thumb near the base of the neck (with or without the bow in my hand). I hunt for a sweet spot around there.
Someone, perhaps Knut Guettler, once said that if you pluck the string where there is a harmonic that note will not sound. Can anyone confirm this? It would account for staying away from plucking at the middle of the vibrating string.
DP