Based on the data from LiveUAmap.com, it appears that the front south of Kursk is roughly 70 miles (112km) wide. A modern infantry division can cover roughly 25 miles (40km) of front.
Yet it appears that this attack was performed with just two brigades - which is perfect for a raid but not so good to take and hold ground.
I’m not sure why Ukraine did this. Was it a spoiling attack? Was it to relieve pressure in the Donbas? Is there some key infrastructure which must be destroyed and a rocket or bomb just won’t suffice? I just don’t know.
The other interesting thing is HOW Ukraine achieved surprise in a heavily contested ISR environment. It could be that Ukraine kept vehicles in Sunny, masking them from sensors. Or Russia just didn’t have any sensors looking at Sunny oblast.
The one takeaway is Ukraine’s audacity. They have displayed an incredible ability to do the unexpected which is making them a very tough opponent.
Pretty good example of "hit 'em where they ain't", attributable to Bedford Forrest or Sun Tzu. Lots of room to maneuver, and they can control RU logistics towards Donbas.
Russia didn't know it was coming, because they don't have the men to defend their borders anymore much less men able to watch what the Ukrainians may or may not have been doing in Sumy Oblast. Not just Ukraine's northern border, but any border, anywhere. They are mostly concentrated in Donetsk Oblast trying to take Toretsk, Pokrovsk, and Chasiv Yar.
The border posts on the Finnish, Estonian, Latvian and Lithuanian borders are empty. If Georgia moved into South Osettia, or Abkhazia for example, the border is almost undefended.