I get more noise with samples per pixel per iteration

I get more noise with samples per pixel per iteration ( useful for multi-GPU ).
Here is my local render, it is just perfect:


Then here is the same at iRendering.net - there is more noise on skin, if you look carefully. It is like a very thin white fabric all over the image…


Settings are just same, except in render-farm I have raised samples per pixel per iteration to 1000 since it makes the rendering goes faster, and it looks even better with 1000 than 500 but renders at same time 17 secs.

Why I get more noise if I raise this higher?