I cannot see what is so important about the nose of the saddle, regarding the positioning of the saddle as all saddles are different, some long and some short. I always take my measurements from the part of the saddle upon which your seat bones rest upon to set my bikes up initially which is usually the widest part of the saddle. Once I get the position of my saddle right, then I take a measurement from the center of my headset to the nose of the saddle as a reference as it is easier then to adjust your saddle if you remove it or alter it etc.
I have two road bikes, both with different saddles, both very comfortable, yet the measurements from headset to nose of saddle are completley different, but the widest part of the saddle to headset is identical on both. One bike has a Fizik arione fitted, which is the longest saddle legal for road racing, whereas the other bike has just a bog standard saddle. Two different saddles, two different measurements.