You're correct in that an occlusion of the paramedian branches of the basilar artery would injure CN VI, abducens. However, since CN VI only innervates the lateral rectus, abducens palsies are horizontal palsies–the eye is only abnormally positioned on the horizontal plane. Recall when during the H-test the eye did not function normally. Was it during horizontal movement or vertical? Choose one of the other nerves or return to the case.