Length Matching rule

Hi,
I've topology for databus like

Driver----------1.Res.2-----------Receiver

Min and Max Length From Dri to Res pin.1 is given.Similarly, for Res pin 2 to Receiver also, min-max length given.
So in EC, in Propagation delay tab,I fixed this min and max length for both the segments.
My doubt is  how to fix rules for length matching within a group(bus) and between groups.
In Relative propagation delay tab, I defined two rules.to fix the tolerance value for the above two segments.I think this will work only for signals within a bus.How to fix length tolerance to match signals between buses?
Under Scope, we've "Local" , "Global" and "Bus".Can anyone of you please explain how to use this?
I gone through the tutorial but still not get a clear knowledge in this.
Your help is extremely needed.
Thanks in advance.