Generally with fruit I'd go 1 lb to a gallon for FRESH/frozen fruit not puree. Puree its more like .75 lb per gallon. For something like strawberries which are rather subtle I'd double that ratio. May want to try that with mango as well. So 10 lbs of fresh mango for a 5 gallon batch or 7.5 lbs of puree.
What is in or removed from the puree that makes you want to use less? I don't use pureees, just curious. If it's just pureed fruit I would think you'd use the same amount - lbs are lbs.