Iceberg resource placement is uniformly one per chunk, with placement not randomised in any way.

Totalchance doesnt seem to work either, or at least, it doesnt work as i'd expect it to.

Iceberg(minecraft:obsidian, minecraft:cobblestone, 33, minecraft:red_sand, minecraft:sandstone, 33, minecraft:grass_block, minecraft:dirt, 34, 150)

I'd expect the above to give a 1/3 chance of spawning no iceberg but in fact it still places one per chunk.

https://cdn.discordapp.com/attachments/630666815533613057/868907449934032896/2021-07-25_18.27.44.png

Seems to work normally. I'm gonna close this issue (for now) unless it rears its ugly head in later.