unexpected hStreams performance

Hey guys, 

I am writing microbenchmarks with hStreams, but I met with some unexpected performance numbers. The observations are that, when increasing the number of partitions (or places per domain), the execution time doubles. Theoretically, I expect the performance should remain the same (or around). Could you help me with the issue? 

I attach the source code and the results. BTW, I am using hStreams v3.5.2.

Thanks,

Jianbin