#I think the MC is supposed to be represented by the crown chakra

[elsyrel]

So, we know that Asra, Nadia and Julian have their marks on the heart, forehead (third eye) and throat respectively. Those coincide with the position of some chakras... so I wondered: where would Lucio, Portia and Muriel have their marks? There are four chakras left: crown (transcendence, spiritual connection), solar plexus (will, confidence and self-esteem), sacral (emotions, pleasure, sexuality and creativity), and root (survival, security and stability).  Taking this into account, I'm pretty confident Lucio's chakra would be the sacral one, Portia's would be the solar plexus one, and Muriel the root one. So here you have my interpretation!