Proper placement of vapor barrier in floor above vented crawlspace.

I just have a basic question. I have read so many conflicting opinions and just needed someone to answer this question: I live in KY which is zone 4. I have a vented crawlspace with HVAC ducts that sweat and run between my fl oor joists in the crawlspace. The sub floor is OSB. I am wanting to insulat e the crawlspace, but I have read conflicting information as to the best pl ace to put the vapor barrier. I read traditionally it is against the sub fl oor. But, then I read if you have a flooring material inside the house, suc h as certain tile, that you should install rigid foam insulation on the bot tom of the joists. But, doing this it looks as if the ductwork in the joist space if it ever were to sweat would cause the moisture to be trapped. Id there anyone that can tell me what the code says, just for my informatio n? I really appreciate it!
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