Is it actually proven beyond doubt that the total wealth or created wealth of the fort affects the number of immigrants in each wave?
My current fort has regularly been getting waves of around 20-23 dwarves every spring. The first year I made very little of any value as I had no valuable metals and was too busy trying to survive, but still got around 20 dwarves.
Last year I made 2 artifacts worth around 500,000 each and still got around 20 immigrants.
I am curious about this myself.
My newest attempt at a 35 level obsidian tower requires me to go slow on wealth. I started with 7 Minors and gave them all farming and brewing. I produced no wealth other than food, drink, and digging.
I did NOT trade with any race during this time. I didn't even built a Trade Depot. I produced 1 artifact.
At the first spring I received around 20 immigrants.
During the next year I made 2 copper axes, and a load of beds, bins, and other wooden articles. I also made 15 tables and 15 chairs, and hundreds of obsidian blocks.
I maybe traded 2,000 worth of trade goods during the year.... mostly narrow clothing that I got from dead thieves.
And I produced a 2nd artifact.
At the next spring I once again received too many immigrants.
I am playing with the Orc mod, but Orcs aren't sieging. Instead I am just getting small groups of goblins. I don't think I have exported enough wealth to garner the attention of the Orcs.
In any event, it really seems to me that I am getting just as many immigrants as normal.
I am beginning to think that the immigrants are based on mining rather than wealth.
I wish I could figure out how to slow it down without tinkering with the init file.