Which preposition to use with assertiveness

of Occurrences 2%

" The new arrivals entered the room gaily with the breezy assertiveness of persons who were assured of their welcome and very much at home.

in Occurrences 1%

We saw this more clearly as the years passed on, and learned how much, perhaps, he had to bear from some of us whose assertiveness in some matters was in the inverse ratio of our knowledge.

Which preposition to use with  assertiveness