I don't understand the use of the tip of a saddle as a measurement point for much of anything, since saddles come in different lengths. It's a fixed point, so it's convenient, but should the distance between a vertical line extending from the BB, or distance from the bars, be different for different saddles?

I think the important measurement would be from, say, the ischial tuberosities to the handlebars or to the vertical line extending from the BB. It may be very difficult to get the measurement from the ITs, but isn't it much more significant that the position of the saddle's nose?

What am I missing?