No and No.
Was King focused on defense when he was lacking flames during imperial archer? No.
Did he take any damage? No.
His defense is legit. There is no trick.
Did Marco attack him while he had flames on? Yes.
Did he take any damage? No.
Did King fail to "activate defense mode" in time? No...
There is nothing to debate about Sen-chan... You just somehow saw something that doesnt exist...