Lateral balance will only be a factor at slow speeds if it is severely out of balance. The main cause of tip stall is from uncoordinated flight ie: a slip or a skid at slow speed. This causes one wing to become more stalled and the tip stall occurs, also a tip stall is the initial stage of a spin. Most sport models do not have a real problem with this if they are flown at appropriate airspeeds. As others have said practice at altitude to learn the airspeed range that is apropriate for your model.