Hi Lewis. I've posted a guide in the Quick Tips section. I've not included any formulas as the best way of working out the length of tape needed is to actually put the tape on the model and cut where needed! (Which I realised as I was working out how to describe the method).
You can PM me if you want the formula, but for all practical purposes, you're better off just cutting your tape to length once you have it in place. Your placement of the tape and how well you line it up will determine your accuracy far better than any calculations. After all, it's unlikely that you will be dealing with a perfect cone, which is what my rather simple method depends on. Any calculation therefore is more likely to lead you astray than give you the absolutely correct answer.
My method might not work if you were doing the nose cone of an F 111 for example. That's got a flat section on the top which throws out the angle which the tape would make with the surface. If your tape isn't lying flat, you're going to end up with creases and gaps. It also changes the distance of your tape from the point of the nose. Masking that would be a trial and error task and maybe, just maybe, you'd be able to make my curved piece fit, but I wouldn't bet money on it!
As long as your object is symmetrical, you should find my method works well enough. Any decent masking tape will allow a little stretching if needed, so that will help make up for surfaces not being perfect flat cones.
Gern