If you cut the throttle and it climbs you need more up thrust because of the trim on the elevator during normal power on flight.

If you turn your plane inverted and it stays level and slightly desends then you need more tail weight or you can leave it alone most people will tell you to invert the plane on an 45 upline and if the nose doesn't dropall of a sudden you are good but i like my planes to be the neutral inverted.