As an example of how precise the circle matching may be, i had a match with 22 participants, 2/3s with dna matches, the rest dna matches to others in the circle. A well known ancestor with many children so I was not surprised to see it. Recently, when I was working on some details to the family, I changed his year of birth to a date I thought might be more accurate based on age range in an early census. Big mistake...my circle disappeared as I suspect I did from my matches circles. When I restored the original and commonly used date, he magically returned a few hours later..whew.