what is the best centre of gravity setup for prop hanging. there seems to be a bit of debate about this. some say move it back or forward or leave it standard.

help

I move mine back slightly so the effects of a full tank of fuel don't make the plane nose heavy until I burn up some fuel.
On the same note I don't move the CG rearward so much it gets hard to handle when the fuel quantity gets low and it's time to land.
Try a 1/2" inch at a time. Or move your battery back 1" inch and see how it handles.

On a 40 size model a 1/2 inch change in CG is a lot. If you are approaching the critical point the model could be come very difficult to control in pitch.

As you approach the rearward limit, make small changes, 1/2 inch is too much.

Every model i have tried to hang has become easier to hang when the CofG is at its rearward limit. In fact my favourite 3d model a Sledge is set up so it is almost unflyable in level flight on an empty tank.

Thinks; must put the tank on the CofG and fit a pump.

Depends on what plane your talking about. A UCANDO.46 can fly fine with drastic cg changes. 1/2 " inch changes are fine.
Certain other planes need smaller changes. .

In my experience, an extremely tail heavy plane may do some 3d stuff better like harriers and waterfalls, but no real benefit for hovering. If the plane is nose heavy it may be harder to hover. I set my CG where if you are flying inverted it takes just a hair or down elevator to maintain altitude. This setting is as good as it gets for hovering in my opinion.

tail heavy condition allows you to do 3-d better.
The best balance I have found is when you are flying a plane, you turn the plane updside down and it continues to fly striaght without having to give down elevator input; it is balanced. If the plane is falling down then it is too nose heavy, if the plane starts to fly upward then it is too tail heavy. Add/remove weight /adjust cg accordingly to get the plane to fly striaght upside or rightside up.

If a tail heavy condition allows you to 3-D better, why not set the C of G at 90% of the MAC? Then, one should just trim for straight and verticle and hover all day long once it is trimmed out.

Balance your plane at or around 30% MAC and you will LEARN to hover with a lot of time and pratice. There is no cheat sheet or perfect setup besides good ole pratice.

A plane does not need to be tail heavy to do 3D well. It's true a nose heavy plane will not do 3D very well at all. By the way, this thread asked about hovering specifically. You can balance your plane so that it flies well (not overly tail heavy where it requires down elevator on landing, won't fly knife edge well, can't fly a straight line etc) and still be able to hover and do 3D well. Practice will have a bigger effect on how well you hover and 3D more than having a overly tail heavy plane.