Regarding depth of submersible pump


We have a borewell that is 700 feet deep and have installed submersible pump (6hp, 20 stage) at a depth of 400 feet. After 20 minutes of pumping, the discharge amount reduces and stays that way. We believe that there are multiple water streams at various depths even below 400 feet. Do we need to lower the pump further to access the bottom water stream or can the pump draw it from current depth itself?

Basically, is there any merit in further lowering the pump to increase the discharge or not?