Advice regarding submersible pump placement in a borewell in Kumbakonam, Tamilnadu

I am living in a village near Kumbakonam, Tamil Nadu. I live in an apartment complex. Even though we have a borewell the capacity of the pump and borewell depth concerns us. With a long term view, we are planning to drill a new borewell with 80 feet depth, 4 inch dia borewell, 3 HP submercible pump setup.My question is regarding the placement of submersible pump underground.

Our groundwater starts at 15 to 20 feet. Our site engineer told me that after drilling 80 feet of borewell, the submersible motor will be installed at 40 feet depth. ie. inside the 4 inch dia borewell the submersible pump will be placed at 40 feet depth and 1.5 inch pvc pipe will be taken out from the pump and will be taken to the overhead tank.

I wish to know whether the placement of submersible pump at 40 feet depth is appropriate. Also if there any general rules that we can follow to know the submersible pump placement?

Any advice will be appreciated.

R Balaji