It's not deep. Atemi does not need weight in all circumstances.
EG: Touch the eyelid of your Uke. Don't warn them! Watch their reaction. That's Atemi! No pain but reaction.
Strike the ribs! Sudden pain and then reaction! That's Atemi!
Strike full power to the side of the neck (please don't do this to anyone unless you are under threat of harm). They can pass out, but not feel anything, as it is instantaneous. That's Atemi.
So KO does not necessarily hurt. Pain is a side effect, if it is felt at all!
There are people who will not react to pain. Shock is what you need to induce!
Remember, we don't have inflicting pain as our goal, so it is unimportant.