Here is a nifty little calculator to work out Centre of Gravity. With craft like the AXN or any that have glide abilities having a slight nose heavy attitude is good.
Once you have CoG, balance your plane inverted, put your CoG mark on the top of the wing.
The AXN will nose dive when power is applied until airspeed increases, wing lift and velocity then takes over. If under speed the noses rises without elevator you have a tail heavy craft and will porpoise at low speeds leading to possible stalls on landing. Again best to have slight nose heavy this can be trimmed out in flight as required.
Be wary of comparing battery weights, I have one brand of 1800 that is the same as another's 2200, I also have varying weighted 2200s from the same brand. So always check and set your CoG to what the plane requires irrespective of the battery size.