How to run benchmarks in betrfs v0.3?

I am running benchmarks in betrfs v0.3 and confused what is the variable that controls the size of the zone. I want to run the exps about filerename and recursive grep with different zone size. But I ran the script(circle-dirscan.sh & circle-file-rename.sh) under benchmark and found that there was no significant difference in results. I need your help.