I had some trouble bleeding the system on my Discovery after a head gasket change, I used the Rave method but I couldn't get the cabin heater to work i.e there was an airlock somewhere.
I traced the air lock to the pipe that runs along the inlet manifold, to get rid of it I raised the expansion tank as high as the hoses would allow and ran the engine till it was warm (without the expansion tank cap) and hey presto, hot air from the heater!
Basically just agreeing with what Jim has already said about the expansion tank being slightly lower.