Graph why were Sanae's mammaries bouncing?
They want attention.
Inexplicable force of ero?
Well, that works too, pick your favorite.
And are we to assume that Utsuho is attracted to the breasts or the armpits?
I would theorize that the armpits have more of an impact, because Okuu has plenty of the other department herself. However, I think she's liking how they work together in a combination... don't you think?
And why did Sanae engage in a ecchi pose during a formal meeting?
We say that the Hakurei miko is naturally gifted, and is strong without any major effort. Likewise, her counterpart in Moriya is... naturally gifted, and exudes that particular aura effortlessly/ unconsciously.
These are difficult philosophical questions, to be sure. I'm glad you're aware of the technical issues to be had in this field.