I'm not saying it's perfect, but the Northeast has obviously had more competitive elections than any of the other regions. This is quite clearly because it has double the population of the other regions.
It's not a huge deal to me, really. But I haven't heard any good arguments against my reasoning.
But if competitive elections are the issue, you'd just end up with a massive conservative bloc and a massive liberal bloc with the Northeast as the only really varied region.
Perhaps a re-jigging of the boundaries of the 4 other regions is in order?