Well, I'm just a newbie, but I think I see Claeyt's point.
Before I really start, let me introduce three terms: x, y, and z. x is the amount of time required by the town owner to complete the largest layer of fortifications. y is the amount of time it took for the owner to earn the assets contained in the outermost layer, and z is the time required for the raider to breach the wall completed by the town owner in x (time). I also know that I should be including another term for the amount of time invested into the raider characters, but I'm trying to keep it really simple.
It's oversimplifying quite a bit, but I think of a hypothetical hermit town that is 200x200 units and fortified with 3 layers of defense between the outside world and the town bell, with each being a brick wall with moderate brazier/torch coverage. It is fully pclaimed over.
So, the person in that town had to build almost 800 segments of bricks to make their outer perimeter if they wanted four gates(requiring 12 blistersteel). Suppose it also has 2 braziers and 2 torches covering each wall segment on this layer, requiring hundreds of wrought iron and over 100 leather. They also adequately flattened the area and farmed over 12,000 bricks and 800 lards.
Now, the often heard but untenable anti-raider argument is "it's not fair that it took x hours to farm or earn the money for 12,000 bricks, 800 lards, 100+ leather, 200+ wrought iron, and 12 blistersteel (assuming they wanted four gates) and it takes a raider z hours to breach the defenses and cost me x and potentially also y time and effort.
Of course, a brick wall doesn't behave like a balloon, and pop when a hole is punched into it, destroying the entire thing. so, it's not like the raider destroyed x hours of work in z hours, but still potentially can do up to y damage. What valuables would be in the outermost (formerly) enclosed area of this hypothetical base? Maybe some canoes. There would be tons of farms, maybe a stamp mill, compost bins, boundary stones, etc. Raiders who got through the outermost layer could do a lot of nasty things (up to y, but probably not really enough as to entirely undo anything close to the x hours of work).
Now, let's consider the next, smaller, but otherwise identical layer of defense. Let's say it took 2/3 of the time required to complete the outermost layer of defense. Let's say .67x. What valuable items are inside the second area? A gluttony food infrastructure? A mine? Alchemy tables (with steam distillers)? Bulk goods(bars, leather, cloth)? Suppose the raiders breached this layer of defense, the amount of damage that could be done is much greater than in the outer layer (y). Let's say 5y time could be undone if the raiders could breach the second layer. Again, this layer is only different from the outermost wall in that it covers a smaller perimeter: it is also a brick wall with each segment covered by 2 braziers and 2 torches. So, how long would it take the raiders to break through this wall? Roughly z? So, by investing 2z, successful raiders could cause up to 6y in damage. However, if they do not breach the final layer of defense, they are not undoing x or .67x, because the walls and braziers can be repaired. So, 2z for ≤6y (realistically, they won't do anything close to that because of the harshness of pclaim drain) and some small fraction of x
Let's say the last line of defense holds the bell (maybe not also the pclaim stone, but who knows) that is valuable in itself and the most valuable items such as profession suits, artifacts, etc.(let's say valuables totaling another 5y). It is 1/3 the size of the outermost layer, but has the same torch and brazier coverage, meaning it took about .33x to make but z to breach. If the raiders breach this layer of defense, in effect, the player will likely lose the entire base (x + .67x + .33x and 11y). It is no longer a strawman argument to say "it took the raiders z amount of time to undo x amount of building!" when they breached the first wall. Effectively, it has been retroactively made a valid argument. Additionally, 11y was lost.
So, first layer breached: z is expended to undo ≤y.
Second layer breached: 2z is expended to undo ≤6y
Third layer breached: 3z is expended to undo 2x + 11y
At a certain point, the cost of z to the defender skyrockets. I think that is what Claeyt was saying.
----I know this is grossly oversimplified, considering it discounts raider character risk and how torch/brazier radii would overlap more and more in the inner layers, as well as the time the base owner put into characters lost in the base, but I think it's a workable example.
