Now that you put it that way, I start to have second thoughts. After reading the description of the attack, I saw in my mind's eye that it would leap in front of Arctucus arms preparing to strike and after landing in front of him it'd swing it's arms. But if instead swing's already on the way while leaping, I'd say Marcus aims the right knee instead as mad one's head might be out of reach. 

Is this change in action agreeable?