Well, while I don't want to say outright that you must be mistaken, I have logged 40+ times with my aim at +1 in Iron Lake and not turned up any Mistletoe. I would normally log longer (and I will continue to a bit more even after posting this), but for you to claim that you ended up with "a lot" of Mistletoe, leads me to believe I would have seen it by now, especially while sitting at the aim sweet spot for Mistletoe. Plus, I did manage to get Sagolii Sage on several occasions even while so far from the sweet spot.
I also saw the yields from a few others that were also logging in Iron Lake, and when they were near me, I never saw a Mistletoe yield for them either.
Do you have a screenshot, or perhaps... could you have been in Treespeak on accident?
