Re: What's the relationship between the height and the amount of charge in the 'waterdrop generator'?

You're correct that the induction takes place between the droppers 
and the inductors. The charge is separated when and where the 
drops separate from the droppers. 

The electric field is an example of "action at a distance"; but you 
would need to measure the distance from the actual conducting 
surface of the inducting cans to the forming drops. Ask yourself if the 
distance changes much as the droppers are raised. I think this will 
depend on the diameter of the cans themselves. 

Part of your paper might want to address this factor.