A program for calculating the strength of the guard on random maps in Heroes of Might and Magic III, called H3CalcGuards.

Simply, avg means that the strength of monsters when generating the map (yes, those buttons located near the water) is average, and the strength of monsters in the zone is irrelevant. This is used for calculating the protection of passages: the strength of monsters in the zones does not matter for them. weak + strong means that either the monsters in the zone are weak, and the monsters at the button are strong (a typical Jebus respawn), or that the monsters at the button are weak, and the monsters in the zone are strong. That is, if you swap the strength at the button and the strength in the zone, nothing will change.

So, 3 chests in MM6A with average mobs will guard the same way as on a Jebus respawn with strong mobs?

Yes, and it will be the same as in the Jebus treasure with weak monsters or as the protection of a passage with a value of 3 chests with average monsters.

And in the center on Jebus, it turns out to be strong+strong.
(in rmg zones on Jebus, weakx4, strong) Did I understand correctly?

Yes, with strong monsters in the settings before generation.