Well, this mod certainly seems interesting in its premise, and I'm happy to be apart of it.

Anyway, I've spent an hour and a half of testing, and while things were generating, they were quite rare. Thusly, I increased the maximum input of "250" in the generation chance to "1000", and trying various 900+ numbers, the generation still remained the same - extremely rare. So, I disabled all my mods and all other map generations, and yet, the same thing still occurs. I don't know if I'm just being an idiot, or I'm actually experiencing a problem.

Regardless, thank you for your time.

Ok...
Mod has 2 separate random generator. First one - when new chunk is generated. Second, works when need to check probability of areas itself.
In other words: If you set global chance to 250 (25%), then every fourth new chunk may be used for new area (+ additional collision checks). Then, if some area has their own chance about 10% - then this area may be spawned 1/40 new chunks.

Also you can check "Area Types" spoiler on forum for additional area details.
Anyway, i'll re-check code and upload update today (with new area).

And what must be:
1% global example: https://i.imgur.com/RurcuXU.png
25% global examples: https://i.imgur.com/FLdbuPh.png https://i.imgur.com/vqtHfDm.png
Game generate 40x40 area around player (1600 chunks), so probability math is pretty simple. And yes, maybe i should increase, a bit, area probabilities and/or global max limit.

I see, thank you very much for your time and effort into creating something for me to enjoy! <3