Mudra 2 relates to the earth and water elements, kapha dosha, lower spine, breath in the low belly.
We've also used just middle fingers touching...fire element, mid-spine, pitta dosha, breath in solar plexus
and just thumb and index fingers touching, air and space elements, upper spine, chest throat, nose breathing space, vata dosha.
Mudra 7 is the integration of all of these things. It is global, whole breath, whole body, whole self.