FSA cranks have no real way to adjust the pre-load. So if you overtighten the crank bolt, it side loads the bearings in the BB and you get more friction. Having said that it's friction on an unloaded crank and there is a lot of debate as to whether this means anything.

If it isn't clicking, and there is no play in the axle then you should be fine as is. Generally I tighten the crank bolt down to the first sign there is any friction so long as there is no side to side play in the axle.

I prefer the Shimano system as it separates pre-load and crank attachment.