Generally speaking rudder offset serves no purpose in keeping the lines tight as there are better ways to do it such as leadout position which yaws the nose outwards. Where it can come in handy is if you happen to lose all line tension and then the model will try to turn back out to the end of the lines. A small excess of tip weight does the same thing by allowing the model to bank slightly outwards. With an old stunter of mine that I use just to have fun with, I've knocked the entire fin (with rudder offset) off it completely by flying a little too low inverted and I've never noticed any difference in line tension on subsequent flights.

With my competition stunter though I've got considerable side area towards the rear and the affect of this in strong winds is very noticeable. On the upwind side I can see the nose turn out which overcomes the wind trying to blow it in on the lines and on the downwind side the nose turns in slightly. So I'd suggest using a fair sized fin with maybe a few degrees of rudder offset (it can't hurt).