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I played this map with the "portal to town" enabled (difficulty level is the same). Overall, the game became significantly more challenging. With the "portal" enabled, the AI behaves more intelligently. It tries its best to combine its forces, creating a powerful hero: a well-leveled one with the largest possible army at that point in time. The remaining heroes of that faction remain with small armies. In the towns that the player captures, almost no troops are allocated for defense; it seems the "main" dwarf takes them. In this case, "Yellow" becomes the most dangerous. There is a certain time limit before which you need to defeat Rolf or Hangwul (this is not related to the described bug). Otherwise, they merge their armies into one (one approaches the other and transfers troops) – it is unlikely you will be able to defeat it. The AI accurately chooses the player's most vulnerable point – the knight's capital and the secondary hero (by this point, they won't have time to escape). The AI sends its strongest hero to this target and also organizes a good "combat guard" – the player's hero is cut off by other dwarves, and in the field, the advantage is on their side. Perhaps all of the above can also be attributed to a map without the "portal," but the spell acts as a kind of process accelerator. In both maps, my main hero is Natalia, and my secondary hero is Mariella. Compared to the map without the portal, the main hero gained one additional level by the end (29), and the secondary hero gained two (30), becoming the main hero.
As a result, I was able to reach Onghair with the main hero on the map with and without the "portal" in the same number of days (1 day, 2 nights, 3 months, although with different heroes), which is interesting in itself, but also allows for some calculations. How much stronger the AI looks can be seen in one battle at the end of the map: main hero – Tolgar.
Tolgar's army.
Creatures level: 7 6 5 4 3 2 1
With "portal": 47 60 99 199 185 358 412.
Without: 39 55 90 195 155 303 79.
% increase: 20.5 9.1 10.0 2.1 19.3 18.2 421
That is, the average (%) increase in the number of creatures (without taking into account level 1 creatures) is 18.1.
These are just numbers. For a complete picture, I am posting videos of the battles (Natalia_Tolgar.sav - map without "portal," Mari_Tolgar.sav - with "portal").
In conclusion: all the benefits from the appearance of the "portal to town" on this map go to the AI; the player, at best, remains where they are.
P.S. I specifically brought Mariella to Tolgar for those who doubt her usefulness.