The study said this:
We have once again conducted wind tunnel tests and computer simulations, and they reveal a strong aerodynamic interaction, especially at the typical distance of 1 to 1.5 meters between cyclist and motorcyclist. The airflow in front of the motorcyclist deflects along the sides of the motorcyclist, thus reinforcing the airflow that the cyclist has to deal with. Consequently, the latter experiences greater air resistance, up to 16 percent more, causing the cyclist to suddenly ride 8.3 percent slower. However, even with a large separation distance of 3 meters, there is still a 5 percent increase in air resistance.