I know he can mold it on the fly, but that's different from "you punch me and my armor sticks to you". He'd have to be actively holding it on Arthur's arm after getting punched in the chest at upwards of 300 mph and violently hurled backwards. If you had written that Adrian is actively focusing to keep the energy wrapped around Arthur's arm, that would be an entirely different situation, but as it is the armor simply adheres of its own accord. There's no mention of any auto-adhesion properties in the CS.