Call it copium but i really don't see any value on seriously defending open fields. My go to plan would be the same as Russia did. Leave a skeleton crew on the front line and have reserves far behind.
Its just open fields, if the enemy exploits this penny-pinching of troops then big deal, they will just gain some kilometres of open field. Next thing you know, reinforcements will come and take that back.
Its really a game of mouse and cat. Don't get me wrong though, if it was anything else than open fields then that tactic quickly becomes worthless as if the enemy grabs a good (terrain) defensive position with minimal losses then to get it back from them you should be ready to suffer x times the losses.
Its all about terrain and its value. Open fields are basically worthless and can easily be traded for other objectives. So yeah, for Russia with its manpower restrictions, having a skeleton crew at this front is relatively ok
Ukraine attacks, Russia retreats, Russian reinforcements come in, mop them up, and proceed to take back the land and possible counter-attack to exploit their defeated and weakened unit formations
I was baffled at how a small force of a few thousand can gain so much ground so quickly. Alex Mercouris released his latest video that seems to make a lot of sense
Here are some points,
1. Initially, the Russians pushed into this area near Kharkov with the intent of of going to Slovyansk. However, they got bogged down due to the mines and the forest. The area has lost its strategic importance. As a result, there were no regular Russian military in the immediate area and only militia from the Ukraine side. Even with that, they were thinly held.
2. As a result, the Ukrainians met basically with no resistance when they go through this area. There were very little actual fighting.
3. The Russians may even retreat out of the Izium area. However, it is more likely they will send in their regular troops to regain it.
4. The regular Russian troops are now just showing up at the battle field.
With the Ukrainians far from their supply lines, it should be very easy for the Russians regular forces to cut them off. I have to say that Zelensky did achieve his objective with this offensive, to change the perception of Ukraine being beaten, at least by the West.