I've always wished manufacturers would be more clear with their directions. (Some of them don't even give a recommended quilting distance.) It seems to me that tacking should be closer together than quilting, since it gives one point of contact rather than a whole line. With quilting it's usually pretty easy to tell if your stitches are dense enough, but not so with tacking. I would err on the side of caution - tack more frequently than the directions say.