Please post your Qs to the LAMMPS mailing list, not to me directly,
so others can respond or learn.
If you read the neigh_modify page, it says the defaults are
page = 100,000 and one = 2000. So your command is actually
reducing the sizes. The defaults are extremely large for most problems
(problem size doesn't matter), so it's likely there is something else strange
or wrong with your problem geometry.
Do you expect your cutoff to induce more than 1000 pairwise interactions
per atom?
Steve