[Mr. Mac]

Bonus balls can double the value of ANY goal score, regardless of whether they are stationary or mobile, so YES you can double the score of a tall tower.
Imagine that the goal is a cylinder with sides formed by the pvc pipe; now imagine that cylinder extends all the way up to the ceiling of the arena. For a bonus ball to double a goal's value it must be MOSTLY inside this imaginary cylinder.
So, for example, if two goals were pushed up alongside one another and a bonus ball was perched up on top between them, it would NOT be possible for the bonus ball to double the value of EACH goal since the ball could not be MOSTLY above more than one goal.