Impossible to say whats a definative right matey, every car is lowered to different degrees, has either good or badly worn out suspension, and different wheels and tyres etc, all of which makes it car specific.

The fitter should know what he's doing to get a good even tyre contact pattern on the road. Adjusting them is simple you dont even need to take them off the car. Just undo the lock nut, extend or shorten the tca to suit, then tighten the locknut up again.

Should pay for themselves with reduced tyre edge wear easily within 2 years, and increase the cars handling at the same time