Wot Nino saya - plus:

There are design problems with the targets - you can try making the stem more rigid, although I have never done this.
The lip that holds the target up can be filed down to make it shorter - be careful!
Sometimes there is excess slop in the bottom linkage - only real cure is better parts which can be hard to find.
Occasionally hooking the pull-down spring from the other direction thru the target hole can assist (if the spring is twisting the target).

good luck!
Ian

So do you think the problem is also that the targets are too flexible - thus absorbing the impact 

Filing the lip is interesting - never tried that !

Great advice Ian