Indeed this seems like a great improvement, but those red squares might be more confusing than helpful in this position.
If I understood correctly, those red squares indicate an open border. But if I were to indicate open borders in this position I’d say that black has open borders at (roughly) J9, J7 and J5, while white may have and open border at G10. So something like this:
The red marks in the actual image would be the most favourable border expansion that black might achieve if white keeps passing indefinitely, so it’s not very impartial.