That is the stratum difficulty he has set.
16+ GH/s - 16 difficulty
32+ Gh/s - 32 difficulty
64+ GH/s - 64 difficulty
128+ GH/s - 128 difficulty
256+ GH/s - 256 difficulty
512+ GH/s - 512 difficulty
1 TH/s - 1024 difficulty
where exactly do you set these values? what happens if they are not set to match the miners operating speed?
Trust me I get an average of 0.003% score no matter the difficulty set.
However I have noticed slight increases of GH speed after the change from 16 to 128 workers.
Bottomline: I get more or less the same score, sometimes higher but sometimes less.
EDIT: You set them from your profile setting under mining