Now that I've had some time to think about it, I would have to agree with Erlik that the problem might be solved my changing the Total Internal Reflection (TIR) setting. It is difficult to say which way it should go especially since I don't know what you have it at currently, but if you have the time try it with a really high and then a really low setting and see if there is a difference in the problem areas. If there is I'd love to hear about it because a solution to this problem would be certainly be useful to myself and others.