Network rendering issues in Softimage

[alias3ds]

Hi There

Why is it that when rendering with User Tools ray3hosts(Distributed Rendering), the more machines I add, the slower the rendering speed will be?
When I increased to four slave machines, the rendering speed was slower than adding only one slave machine.
I'm using a full gigabit network. Could this be related to network bandwidth ?
Any help would be greatly appreciated.

Alias