See notes on Boost and Possessor Demons for information on exceeding your Stamina by more than x2.

"Stamina" and "Will" are not "body" and "mind."

Stamina and Will are both physical and mental phenomena. When your character looms physically to intimidate someone, that's Will. When your character calls upon memories of childhood abuse to draw upon hate in order to heft that portcullis, that's Stamina.

Stamina = impact on, influence over physical motion.
Will = impact on, influence over personalities.

Both draw on whatever physical and mental reserves are necessary for these effects. [1]