I don't know if they're that contrived. The scenario is that you have a closely matched two party system (as most FPTP places do) and a third party which is clo

I don't know if they're that contrived. The scenario is that you have a closely matched two party system (as most FPTP places do) and a third party which is close in popularity to one of the mainstream ones on first votes, but is not universally supported by the remaining mainstream voters over the other mainstream party. That doesn't just sound plausible, it sounds like exactly the pattern of growth for a third party that you'd expect.