Good stuff.
I use bottom buttons exclusively. Though I feel the GP has the best button of all, the ELA fires smooth as well. I grip the ELA with my thumb, index, and middle finger. The bottom of the ELA rests on the middle knuckle of my ring finger, and firing is just as snork stated, a contraction of my fist MORE THAN an intentional move of my finger.
I like gripping the lower half of the mod anyways because if using a KFL it keeps me from accidentally plugging the air hole.
Before I finished that above statement, I almost typed "gripping the tube" in the first sentence, BUT I'm well aware of the kind of "minds" we have in this thread, and that would have birthed about 36 posts referencing "tube gripping".