[distribute_scans]: Call .size instead of .count to distribute work more equitably

I don't understand the difference between count, length and size very well.
Don't want to bother either ( its midnight !). But for those who care, perhaps
the following might help

Ref: http://web.archive.org/web/20100210204319/http://blog.hasmanythrough.com/2008/2/27/count-length-size