OP doesn't understand the program/script.

I used your single key check and it didn't even find a match.

Check it yourself:

With 4,000,000 keys in database I ran this for a single key check.

pk = 3093472814 - 62500

No results.

But I think I figured it out.

Whatever pk is landed on, whether random or increment, it has to be a multiple of the collision margin.

because if you run single key check using:

pk= 3093472814 - 3999936
pk= 3093472814 - 640
pk= 3093472814 - 64

you will get a match.

I'm even more lost now lol.