It’ s already more extensive than that.
The second encirclement, west of Mikolayev towards Kiev, is sketching up quite clearly.
And I doubt Russians will ignore Odessa.
So what would possibly remain unoccupied is the truly western Ukraine, only it won’t make sense, militarily speaking, to leave a thorn in the side.
Anyway, the double encirclement will have as result a complete suffocation of the Ukrainian army.