Walkthroughs for custom maps.

It’s good that you wrote that you figured it out, because the FizMIG doesn’t describe the specific behavior of monsters when a firewall stands between them and the stack being attacked. It only says this:

Two-hex creatures take one damage when passing through fire, and if they stand on two fires at the same time, they take double damage. Also, neutrals can clearly see the firewall and easily bypass it if possible. Sometimes, neutrals may change their priority target if the firewall prevents them from reaching the first target.

For me, this is also a mystery, but I know that there are maps with spectacular battles where quite large monster squads are killed precisely because the player forces them to pass through the fire several times.