Of course, the system itself can distort which voters get a voice, distorting what the centre converged on is, and hence each country's policies will be built around a different centre.

I guess "converging on the centre" basically implies that the electorate is fundamentally fractured on one axis. (Rich/poor?) In theory states where another consideration is important (e.g. Scottish Nationalists?) the centre might not be converged on in the same manner.