I hereby officially doubt the common formula to find rustroots.
It is said, you need at least 4000 as a result of perception*exploration.
Some suggested 64*64 would be enough.
How comes I found 2 (and probably more in the future) with only 750?
I only got 16 Perception, but 47 Exploration. So I dare to say its Exploration that counts. This way, of course, people with more than 50 Exploration will definitely be able to find rustroots. I wandered around the forests for ages, never finding a root and believing it is because I just don't have enough Perception/Exploration. Yet, the only thing I ever raised these days WAS in fact exploration. Not perception, not intelligence or any other attribute.
Comes to mind, maybe Loftar heard the cry of his lambs and decided to make it easier to find roots