I'm not familiar with double the distance method. I'll check it out on Dave's site. To be clear, I differentiate between an aiming method (CTE, double the distance, contact point, ghost ball, fractional, bracketing, using ferrule edge, etc) and the final reference (which can be the contact point, ghost ball, aimpoint, edge of CB or OB, rail, entire OB, light reflections on the OB, etc as described by several others in this thread). Some methods such as contact point and ghost ball explicitely describe the final reference but not all methods do (such as CTE which is why I asked the initial question). I do this because the method is mainly mechanical and although it does play an important role in your shot routine, the final reference is central to the final focus point which plays a key role in your ability to execute the actual shot with precision and consistency.
I can use several methods to find a reference aimpoint (CTE, ghost ball, pure feel, bracketing, etc). Once I settle on a method, similar to settling on using a reference aimpoint, I will use only one to be consistent - I never use multiple methods or reference points. Also, although I use the term 'aimpoint at the base of a ghost ball' to describe where the aimpoint is, I don't use the ghost ball aiming method. I've never been able to visualize a ghost ball. I can and have, however, used training aids to see where the aimpoint is.
With regard to the 1/8 inch spot, note that's what I train with, in actual practice I pick out something physical in the cloth located where that 'spot' would be. So it's the edge of a chalk mark, a discoloration in the cloth, a part of the cloth itself that stands out, etc. Even on brand new cloth I've never had a problem picking out a mark or object that works.
I've tried the fractional edges before as reference points and I haven't been able to make it work for me. Perhaps I'm lazy but the aimpoint is working quite well right now and I think it's possible that the process of using CTE may help to validate the final reference aimpoint providing additional confidence in it's selection. I won't know until I try it...