Cocos2dx - setVelocity works differently on other

Question

I'm dying with physics , i've tried to use setVelocity however i got slightly different result from different devices.

I've tested on iPhone 5 (on simulator) and iPhone 6 (real device) The Director::getInstance()->getOpenGLView()->getFrameSize() returns both devices is 640x1136 pixels

But i see they have different result after the animation , its about 2-5 pixels. I really don't know why.

I'm making a multiple player game so i need exactly same coordinate of objects on every devices. Does cocos physics return randomly result?