Yep, that's it - asteroid orbiting is off, I just forget to turn it on somehow.
But I thought, asteroid belts generated as belts, not spirals...
And this symmetrical pattern generator persuades me today:
Yes, that's nice too. But how?!! I didn't do it!
UPD. Understood. There is not an exactly symmetrical pattern and they are moving now from previously surveyed points, that are just between those 6 vertices.