Correct…
No… input side. The Multi tries to keep its input at zero (or whatever you set as the setpoint), and it will charge or discharge the battery in order to keep it that way, until the battery is either too low (MinSoc) or it is full. But close enough…
Not only excess. It will use battery energy as well. The philosophy is that it tries to keep your grid import as low as possible for as long as possible.
The ET112 merely moves the measurement point. The system makes no distinction between input/output side loads when it decides how to minimize your bill. The distinction only matters when the grid fails… then only the output is backed up.
I know there are people with use cases where they want power to be fed back to the input, from the battery too, but not always… the use case is specific, and best implemented with something like node-red. For now anyway. It is now part of the Venus 2.90 large image release.