Maybe can be rationalised if consider airflow's Velocity rather than Volume rate
Possibly a universal graph for Effectiveness vs Velocity can be produced
Attached revamped Post 58 Graph2&3 (m/s=(1.22 >>1.3)xm^3/min)
Very unsure whether is universal as regards radiator area and volume.
Car Radiator zone is that investigated by
Delphi
Possibly,with quieter engine development(dunno whether electric vehicles have a rad), the car radiator industry will further enter the PC zone
Dunno how realistic Zones are.