“This would make it similar to the classic Mongol tactic of the feigned retreat, with large forces lying in wait for the pursuing enemy to tire themselves out.”
It’s an ancient, tried-and-true tactic. The Oglala Sioux used it against US troops in Wyoming in December, 1866. The tactic resulted in the utter and complete annihilation of the Fetterman column (which the Sioux referred to as the “Battle of the Hundred in the Hand”).
So once the Ukrainians have surrounded them the Russians will have them right where they want them