Dug-in bonus not showing?

[Antiochus_Soter]

I am playing in the 1880s. When I attack the enemy they seem to have a dug-in bonus that gives me a -4 on the battle screen.

However when they attack me I see no dug-in bonus, even though before the battle starts when I hover over my unit it says "dug-in 1/1: 5 days for next dug-in bonus".

So my questions are:

1) If before the battle starts I have a dug-in bonus of 1/1, should I not get at least a -1 to their attack once the battle starts? Why does the dug-in icon not show up on the battle screen then?

2) what proportion of my armies have to be dug-in to get the dug-in bonus when the battle starts? Say if I have a 15 stack in the province that is dug-in and then I send in another 5 stack to reinforce the province right before the battle starts, do I lose the dug-in bonus because the reinforcing units does not have time to dig-in?

3) Does my enemy get the -4 to my attacks because they have some tech advantage over me? If so which techs do I need to research to get higher "dug-in" bonuses?

I am playing with the AHD extension but without HOD by the way.

 

[TK-XD-M8]

You can research it with the same tech that increases fort level.

 

[Kovax]

The left-most tech on the Army tech tab includes defensive bonuses, including the "dug-in" bonus. High scouting ability can reduce the dug-in bonus, I believe, so if you have no cavalry, you'll be facing the full penalty. I also suspect that leader traits can affect the odds of suffering the terrain penalties, since there's a semi-random chance of the battle occurring in different terrain within different provinces. Bad leader + bad techs = bad odds.