Interesting thread - I've often found myself in joining in the overhead, as per instructions, descended deadside and got stitched up by pilots joining on crosswind (but not over the upwind numbers), and others joining downwind. Add to that some aircraft with high climb rates coming towards you (the worst combination the lower aircraft high-wing, and the higher a low-wing)
Given that sort of congestion it shows our good standard of airmanship that I can't remember any mid-airs in that phase of flight.