Different techniques are required to flick (or snap) different types. Important to find the "sweet spot" for the elevator. I've never flown the Robin so these notes specifically don't apply to that. Some types just flick so nicely and others just don't do them nicely or require a particular technique to get them to work at all.
Neil's pear-shaped flick was in a Stampe, which I also have not flown but offers would be welcomed. The Pitts is one of the best flickers there is (not counting the S-2B which takes a special method and you need to hold your mouth the right way as well).
First time I flew an S-1S I couldn't do an ordinary loop without stalling it so stuck to avalanches after that.
The Cessna Aerobat is another nice flicker - hold the yoke back all the way around; wind in full aileron in direction of roll if you like, but only after it has started to roll. To stop - use everything - a double shift of the yoke from side to side(i.e. aileron) is needed at the end to stop the wobble and stop neatly on line.
stik - did you try hauling back on the stick as you came upright with those avalanches? - it needs some persuasion to go around a second time at the top of a loop.