City Entrenchment Question

[demyansk]

I have a brief question. What is the background of always giving a unit a level 3 of entrenchment when in a city. it seems that when units are retreating they always get that level 3 in the city. Sometimes, I think its unwarranted but I do understand that a city does offer the ability to entrench. However, as stated before, it seems that all the time is unrealistic. Oh well, still love the game.