One corresponding offers two similar endorsements, one deficient (3-1-3)
I believe the answer is:
vis-a-vis
'one corresponding' is the definition.
(vis-a-vis can mean counterpart or opposite number)
I don't understand the rest of the clue.
(Other definitions for vis-a-vis that I've seen before include "In relation to, as compared with" , "Facing; in relation to" , "With regard to" , "Face-to-face" .)