Well. Coilovers, for wan't of a better phrase, are a unit.
Damper plus spring on an adjustable thread.
So at its maximum length ( or whatever you have it set to ) should be long enough to support the wheel with the full weight of the car, and not rub the arches.
Do your wheels rub the arches? How much of a gap is there?
The only way the strut would be loose is if the wheel was right up in the arch and the top of the wheel was resting on the inner arch, thereby taking the pressure of the top mount, and instead putting it onto the top of the wheel arch. Unlikely.
I suspect that you've just wrongly fitted top mounts or loose strut-to-hub bolts.
Unless someone else can enlighten you.