Consumer 1.75" Shell Break Heights and Widths?

[Wrecktangle]

Having a hard time determining the optimal angles to set the tubes in a fan rack. What are the typical heights 1.75" consumer artillery shells break at? I know effects are different resulting in different widths, but what would you figure an average break width would be? i.e., Mega Banger Exterminators and World Class Fireworks Excaliburs.

[Carbon796]

A very general rule of thumb is 100' per inch.

[Wrecktangle]

Thanks Carbon!