Sorry it took me a while to answer! Getting ready for the webinar 🙂
So, you’re correct that Spleen is the Tai Yin meridian of the foot, but it is part of the Yang Ming Circuit. The Yang Ming Circuit includes the hand and foot Yang Ming meridian (ST and LI) and the hand and foot Tai Yin meriians (SP and LU). We name the CIRCUITS by the Yang meridians because it is easier to see what zone of the body the Yang aspect of the circuit flows through, in this case the Frontal Zone (Shao Yang circuit is Lateral Zone, Tai Yang circuit is Dorsal Zone).