Do not ask me to explain, I have documented proof that my Structural Design skills should not be trusted so I can just parrot words "unless your external repair is stiffer than the original tube, you get some bending at the repair, once that happens you are concentrating loads at the original break on a repair that is weaker than the original tube. After that, you get cracking and finally the repair fails. That is one reason you want to use a piece of the original tube as an inner sleeve, properly done, this bends like the original tube so you are not concentrating the stress...... If you use a repair that is much stiffer that the original, the tube will bend at the edges of the repair causing cracking and failure"

Don't take this as any gospel, the standard methods are probably way overkill.

My method is to try a tapered joint with a external sleeve. If it breaks at same point again, redo it with an internal sleeve. The exception to this are masts. With masts I use everything I know and try not to dream up stuff that will make things worse.