For example, they added the weight and complexity of a heat pump to the BEV because they realized that those pounds were a worthwhile sacrifice to achieve a range increase.
While I agree that the opening in that panel looks terribly inefficient, it doesn't make much sense they'd leave a big, drag inducing hole that could have been plugged by a BEV-specific $1 vacuum-formed underbody tray.
From Technical training, Product information, I01 Heating and A/C Systems:
The heat pump heat exchanger is installed in series between the coolant pump and electric heater. The energy consumption of the electric heating is reduced effectively by using the heat pump and can be saved under certain circumstances.
In the following efficiency comparison it is clear how high the energy saving is with the heat pump. In order to obtain about 5 kW of heater output, about 5.5 kW of electrical power must be used for the electric heating due to resistor losses.
A system with a heat pump only requires about 2.5 kW of electrical energy in order to provide the same heater output of about 5 kW.
The EKK consumes this electrical energy in order to compress the refrigerant and generate the heater output at the heat pump heat exchanger.
By using the heat pump electrical energy of up to 3 kW can be saved in favorable conditions. This energy can then be used for the electric motor of the vehicle, thereby increasing the range.
The heat pump is not an individual component, but a complex adaptation of a refrigerant circuit with an equally complex control structure.
The highly complex system of the heat pump, adapted to the heating and air-conditioning system, places high demands on the workshop personnel during diagnosis, but when it comes to its application the customer is unable to distinguish it from the conventional heating and air-conditioning system in I01 with the range extender.