I'm jumping into this discussion a bit late, but I sorta disagree with your statement that there is no natural air flow through the radiator. I've always understood the that Mini's left front wheel arch generates a low pressure area at speed, so the air entering through the front grill of the Mini is naturally drawn through the side radiator into that wheel arch cavity. The fan, of course as with most cars, is only necessary at lower speeds, or when stopped, to help maintain the air flow through the radiator.
Also, the reason for the switch to the front mounted radiator in the Mini's last few years of production was not to improve cooling (although that may have been the result), but instead it was done to comply with increasingly stringent EU drive-by noise standards. The Mini's exemption ran out, and Rover/BMW were forced to finally mount the radiator behind the grille to achieve a quieter drive-by noise level.
