A starship does not have to be streamlined to operate in space. It could be a perfect sphere, an irregular mess of random shapes, or an ungainly blob, and it will work as well outside of an atmosphere. For this reason, spacecraft generally are built as efficiently as possible, with little concern for where exactly parts are bolted on.

The big exception to this is if a ship is required to make planetfall. In such a circumstance, the ship will need a shaped hull, probably symmetrical, and with considerable thought given to aerodynamics. The result of this is a loss of efficiency.

Five slots are required for streamlining. While this does include lift rockets, landing gear, and heat shielding, the bulk of these slots contain…nothing. They are just an expression of the inefficiencies resulting from making the ship more streamlined—the price one must pay to be able to land on a planet and take off again.