From what I've seen and mathed, the rate should be something around ~15-20% to get 1-3 MCDs, and on average you'll get 2 MCDs. So, expected value is ~0.3-0.4 MCDs per tool desynth. For reference, the person who said that he was getting 2+ MCDs per 9 tools, the expected number from my maths says ~2.7-3.6 for that many desynths. So, that guestimate of ~15-20% is definitely in the right ballpark.