I think the smallest clearance I have is on the carbon bike, and that is about 1cm. I don't think a small clearance is a big deal unless it causes your feed to rub the chainstay when you pedal, or if it is SO close that there is a danger of the crank arm rubbing the frame if you everything was flexing during a hard effort. As long as this isn't the case all you need to worry about is proper chain line.
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