It stacks, i.e. it's better to have 2 small FC rails than one. I'm not sure where the max limit is reached, but IIRC it's around 2 smalls or 1 medium FC rail. If you have 2 medium rails it might be best to make the other one a superpen.
I'm pretty sure 2 small rails are slightly better than 1 medium for FC purposes, but I don't think the difference is all that large. In practice, the effectiveness is largely driven by good timing on the part of the rail shooter.
I'm pretty sure 2 small rails are slightly better than 1 medium for FC purposes, but I don't think the difference is all that large. In practice, the effectiveness is largely driven by good timing on the part of the rail shooter.