I had asked earlier for a clarification about when a unit is considered in terrain.
The answer was when at least half the unit was in the terrain, as there are no rules for column etc, which made sense at the time.

Having now played a couple games under that definition we have run into a problem.

It makes it impossible to use two terrain pieces to block a flank, they literally have to be placed touching. By the letter of the rule, if there is a gap between the two pieces and a unit keeps its center point in that gap it is technically not halfway into either terrain.

I was rather surprised when I set up the terrain and used a woods and a rough about 3 inches apart to "seal off" my right flank and the opponent was able to march a two unit wide line through the gap without paying terrain costs

Thoughts?

but entered the wood with a group line as one of the Unit was out and the other is (half group out and half in)?
If so it is wrong as the terrain must be calculated on the single Unit.

Anyway if you want to cover your flank with a terrain you have to leave less than half the base width as space between your Unit and the terrain piece.

But if you want really cover the flank use an impassable terrain as troops cannot cross them, even partially (in Impetus is more explicit).
You can depict an impassable terrain also with a wood or a rock. Impassable terrain is a sort of exception to the terrain rules.

Was like in the left side of the pic below


Both units had less than half a base into the terrain, I suppose this is where your idea about simulating column movement comes into play.
All well and good.

But the situation on the right side is where it gets odd. In order for that unit to be affected by terrain the two terrain pieces would have to be touching.
Just making sure that is what is intended. You will have to forgive me, but we've been playing DBA a long time and it has taught us the bad habit of dissecting rules

from your picture (on the right) I would say that the Unit is on terrain as more that its half surface is on it.
Anyway to avoid these cases I would suggest to leave more space between terrains or place them in contact. Otherwise you have to calculate for every squared mm!!!! In case of doubt roll a die to determine if the Unit is half on the terrain or not and save time for game play

Oddly enough that is the conclusion we came to
Nice to get your opinion though.