@ Tom and Paul
The car is much better balanced in the air with the rear wing mounted as far forward as possible (and little/no guerney), which means you need to trim a section out of the front of the wing. Like;
http://www.oople.com/rc/photos/south.../NO5E1237.html
Up to you like but if it jumps nose high move the wing forward and cut the back out, same with understeer into a corner at the end of a straight (Worksop for example).