> converges over 3 bars bars of what length? a 3 against 4 polyrhythm converges after 12 beats, so here it's 3 bars of 4 beats, which is a "bar" for the second rhythm you passed in (`'4-x'`) but four or two bars for your first rhythm (depending on if you write it 6/8 or 3/4, this one could go both ways). Would be worth letting us know in the CLI, if you think about more esoteric polyrhythms it gets more confusing.
4/4 is the default.