There were nearly 20 people lurking on the north side of the factory...
Before Mountain Eagle initiated the surprise attack, they had been waiting for Mountain Eagle and his men to take the initiative to attack the factory.
Bolonicov had planned it well, as long as the enemy was lured out, even if the factory was short on manpower, they could still hold them back.
When the time came, the twenty men from the north, along with the real reinforcements from the south, could encircle the opponent from three directions and exterminate them within the factory.
Unfortunately, Bolonicov's tactical wisdom had reached its limit!
The way Russians fight really has nothing to do with 'flexibility'...
Not to mention Bolonicov, a layman; throughout their history, since World War II, whenever they faced an enemy adept at flanking and interweaving and the forces were not drastically unequal, they were always beaten severely.