Whatever you're trying to do with the topics now is ham-fisted and clumsy. It's far, far worse that the occasional bad topic slipping through.
I agree with Crash. I think the current proposed topic formula should be chalked up as a failed experiment.
But being the helpful type I am, I'll propose an alternate model (nicked from what I consider the best internet discussion board out there):
Short topics, early closing and no topic ressurection.