Umm you sure about that.
I understood the even on the original model the dripper was controlled.
Either that or the laser has to cover the entire surface of the print vessel for every single layer. Which would set a specific print time per layer that would allow any part of the surface to be printed.
Otherwise it would be impossible to print different things on each layer - the very definition of 3d printing.
Either way you can print the entire surface per layer.
And the resin must be less dense than the water otherwise the whole thing just would not work.