Oh geez, so it's me again 
The neighbors algorithm is dependent on the extent of the sprite that asks for them. I'm currently too lazy to look up the specifics in my code, but the rule is that there's some relationship between the sprite's area to the surrounding box that it scans for neighbors. The neighbors attribute is meant not so much to perform statistics on surrounding populations but to narrow-down potential collision candidates, or to find the nearest one. If you want a configurable circular view of "neighbors", you can use something like this:
