Speed and aggression.

The strength of the guards on the two short passages between opponents is 6000, to prevent overly rapid contact.

Forgive me, newbie, but I've lost so many times specifically on this guard post... There are 10-11 Fanatics with 6000 strength (which is manageable), and an 18-19 strength Necromancer + an 80% upgraded stack (or is it just me?). And these, excuse me, are different things...
That's why I've started treating these creatures with increased caution...