Andy,
On older spindles the steering arm bolted on, providing the connecting point for the tie rods. Most IFS it is the steering knuckle, forged as part of the spindle assembly. The geometry of the steering arm/knuckle affects the turn ratio, speeding it up or slowing it down in proportion to the distance from the spindle centerline. Lock to lock vs travel length gives you one part, but travel length to degrees of turn is another piece of the puzzle as Dave points out. Your way will let you compare racks which may solve your problem.