“On the wall of the altar” — the lower wall; the wall whose residual blood is pressed out toward the foundation (yesod).
Type of Learning: Diyuk linking “kir” to the later phrase about residual draining: the application point must be the lower section so that leftovers naturally reach the base.
What Is Learned: Blood is applied below the red line (the midline of the altar wall). After the sprinkling, whatever remains is squeezed toward the yesod; the lower placement makes that draining coherent.