The article says there’s a narrow corridor which is about 0.5-1 km wide. This means the Ukrainians are in operational encirclement.

Russians usually leave a small corridor open like this, because they’ve observed that Ukrainian high command dislikes retreating and insists on sending reinforcements and supplies, as they order units to hold to the last man. At the same time, they try to sneak out heavy equipment and elite units. Both resupplies and shuffling of troops/equipment along this narrow path are usually easy targets for UAVs, missiles and air strikes. That’s when they inflict the highest losses. This also softens the units caught in the pocket and makes capturing them easier and less dangerous.

The fighting in Pokrovsk and Toretsk indicates that the ukrainians probably retreated some if not all of their elite units from Kursk already. Either way we’ll probably see Sudzha and Kursk back in russian control by the end of the month.