Not sure I follow. If you get net hits, that means you got more hits than the defender, so you hit them, which means they can't evade the grenade. If, on the other hand, your attack roll doesn't beat their defense roll (you get the same amount of hits as they do, or they get more), the grenade scatters the full XD6 meters (1D6 if thrown, 2D6 if thrown and aerodynamic, 3D6 if fired from a grenade launcher) before exploding, and that amount of scatter will be how far the direct target is from the grenade when it explodes.