For those questioning how Mendy and Sane fit into the same team, pleaser refer to Walker and Sterling.
We'll see Sane come inside much more often, assisting less and scoring more. Look at Sterling's and Sane's combined goals+assists this season. Sterling has 20 + 10, Sane has 12 + 15. Sane has been maintaining width on the left because Delph plays purely as an inverted full-back. This often pushes Kev further right, with Sane and Walker providing the width, with Sterling moving inside as the second Centre-forward.
With Mendy on the pitch, You will see the same movements on the left hand side, with the triangle of Mendy/Silva/Sane operating the same way as Walker/KDB/Sterling.