I'm putting this here to better help new players. Feel free to clip any other spots where I posted this please mods, or leave it. It seems it's pretty helpful from all the PM's I'm getting.
This guide is so people better understand the 1/N base damage for defensive structure groups.
Okay, I've had a nice long chat with Jorb. here's how this works.
1. Spammed off claim braziers and torchposts are known to them and are hopefully fixed by the time you read this.
2. Empty and damaged braziers are now included in the damage group but they are thinking of changing that.
3. Brazier range is 23 hexes approx. and torchpost range are the damage reduction range for them.
4. Base damage is 40k bb for a group of brazier/s, less for torchposts. A single brazier will do 40 bb, 10 braziers all within range of the attacker will do 40/10 damage each so 4 per brazier. The base brazier attack of 40k bb is not a fixed number. Jorb has confirmed that it is 40k but it is a randomized number based on several factors. It's possible that 40k bb is the average attack amount while using only braziers.
5. Torchposts and Braziers are part of the same group damage calculation so nearby torchposts will actually lower the max base damage of the group.
6. Damage is determined individually per brazier/torchpost at the time of firing. The damage each brazier/torchpost creates is determined individually and reduced by each brazier/torchpost within range to the firing brazier/torchpost.
7. Example one:
In this example the square is the attacker and the circles are braziers. The first brazier fires for 40/2 = 20bb against the attacker as it individually calculates only the second brazier within it's range. The second brazier fires for 40/3 = 13.333 bb as it's within it's own range of 23 of the first and third brazier. The third brazier is not in range of the attacker and does not help the group base attack, it only hurts it. The attacker takes 33.3333 damage instead of the 40 if only the first brazier existed.

8. Example two:
In this example a line of 35 braziers is attacked by the attacker represented by the squares. If the attacker was the red square and he attacked the brazier in front of them the right most
30 braziers would be in range and fire. The right most brazier would fire for 40/23 = 1.739, the second right most brazier would fire for 40/24 = 1.666, the third brazier from the right would fire for 40/25 = 1.6 and so on along the line. Each individual brazier to the left would have more braziers figured into it's damage base up to the middle one which would fire for 40/30 = 1.333.
If instead the attacker attacked at the yellow square then the
23 braziers on the left side of the line would be in range and attack him. The first brazier, the one in front of him would calculate at 40/23 = 1.739 bb, the second brazier to the right would calculate at 40/24 = = 1.666 and so on. The point of this being that the attacker should attack in range of the least amount of braziers or in range of the least amount of braziers who themselves are within range of the most amount of braziers.
If instead the red square was the initiating first attacker while the yellow square was secondary attacker after the red attacker had already come under fire then the red attacker would come under fire from the rightmost 30 braziers and the yellow attacker would come under the fire of the left most 5 braziers.

9. Example 3:
In this example the red square is the attacker and he is attacking between two braizer groups that are both in range. Each brazier is far enough away (23 hexes) from each other that they both constitute an individual group. The left brazier would fire at 40/1 = 40 bb and the right one would also fire at 40/1 = 40 bb. The attacker would take 80 pts of bb damage if he attacked at that exact middle spot.

I hope this helped a little. I'll take any questions in PM if you have them.
Base design is mighty changed from last world. I'm seeing that you'll have to balance coverage versus detrimental braziers to the point of attack.
Edit: Jorb has mostly confirmed these calculations. He did correct me in saying that the 40k was not a fixed number but rather is randomized. We don't know if that means 40k is the average or that if it means that it depends on other factors. Here's the quote:
jorb wrote:Apologies. The base damage is 40k, but I realize that this number doesn't mean much to you as damage is then randomized and combobulated in more ways than one to arrive at the final number.
Edit: Jorb used the number 11.5 for some reason for base damage determination I thought. The radius of the brazier (23 hexes) is the determining factor apparently.