I'm only a few weeks at target so hard to say. The official line is that you increase your Healthy Extras one at a time until you hit a level that works. The reality I guess is that you just mess around until it levels off. You are allowed +/- 3lbs around your declared target before you have to start paying (and you have a weeks grace if you go outside the zone to get back in it)
To be honest, I havent really changed much at all, I'm still following pretty much all the principles, still sticking to 5-15 syns a day, but having occasional days when I go over syns (pub, meals out, takeaways etc) - but then I always did.
So far since hitting target, my weigh-ins have been:
1st week: +3lbs (was at Centre Parcs and ate loads of puddings!)
2nd week: missed week (dont have to go every week when now I'm at target and had to be somewhere on my regular SW night)
3rd week: -4lbs (lost all that center parcs weight, so 1lb under target which is within the allowed zone)
4th week: STS (so 1lb under target again)
I really dont think that I have changed my approach very much at all so far, I guess I'm just slightly more relaxed about treats, going over syns allowance, or eating a bit more bread and cheese.