Funnel, transformed to unconstrained space

Just a quick comment. Joint mode and funnel can even have the opposite behavior: as I showed in my simulation, in models quite like “Gelman’s funnel”, increasing group variance eventually eliminates funnel as tau is kept away from 0 but also leads to bimodality, in contrast decreasing group variance will avoid bimodality but gives rise to the funnel/metastability/slow mixing of HMC chains.