I have 3 siblings, and of the 4 of us there are four of our known great grandparents who, when you compare pictures of them with, each of us, there is a striking resemblanc. I look so much like my mother's mother's mother. My brother Paul looks so much like her husband that you'd think Paul was his son. My sister looks like my father's mother's mother. My oldest brother like my fathers mother's father.
Perhaps that's a better estimate of dna input than the paper.
Nevertheless, the paper estimate must be useful, it is at least instructive of a place to start.
My brother did the ydna only. I think its time to go back and take the big test at ftdna.