If you want to permanently fix this "overlapping" problem, all it takes is a slight unannounced nudge from your back wheel to their front wheel. This happened to me once, and I'm cured of ever drafting like that again. Mind you, it was totally by accident, and I was with a friend, but since then he's learned to signal before a turn, and I've learned to back off in case he forgets. It took a couple of weeks for my a$$ to recover from the road rash.

(Note: I'm not recommending intentional injury to another cyclist. I'm just saying, if you did that, you'd only have to do it once.)