Oops, you are right. I was mistaken about the comb filtering part. (That's what I get for posting before I've had my morning coffee.) But mismatched mics
will introduce phase problems none-the-less.
Perhaps this article will help.
http://www.soundonsound.com/sos/may06/articles/qa0506_1.htm
This is a quote from YEP over at the Reaper forum on the same topic.
"...having one mic peak +2dB at a certain freq, and the other mic dip -2dB at the same freq could be a significant problem. Notes that resonate at that frequency might appear to suddenly move to one side, room sound and ambiance might feel unbalanced or acoustically "wrong", setting balanced levels might be difficult, and so on."
Another thing to consider is that large diaphragm mics tend to capture less off-axis HF than small diaphragms making them a poor choice in general for overheads.