I would follow the manufacturer's recommendation for how far apart you can quilt/tie for their particular batting. Different battings have different requirements. If the package says "can be quilted up to 6" apart" then I would go no further apart than that, for instance. I don't think there has ever been one standard spacing for tied quilts. If there are no recommendations available, then possibly keep your ties to within 3-4" of each other just to be sure it doesn't bunch later when washed.