Maximum hydropower is available at the 2/3rds point for dynamic/static pressure.
furthermore the efficiency of your turbine may be highly velocity dependent, particularly if your generator is rpm locked to the battery voltage.
I would measure the mechanical power with a pony brake while adjusting the nozzle diameter, then design the generator after that. hope its close to what you have now but you may find twice the power available if you match the rpm correctly to the turbine and nozzle. if its a pelton or turgo, you can change the number of spoons of course.