wing drop
Hudson
I don't really understand the reason for not refering to maintenance if the aircraft is not correct rigged. A quite simple adjustment to do. More likely, if your description is so correct, it is to do with a twistered fuselarge which will not be practical to fix, almost impossible in reality.
Experiment with a clean stall, power at idle. Does it drop a wing while in balance. Then with max flap again at idle. It is possible to do a small adjustment to the wing incidence. Flaps may also be adjusted independently. Eigther could be the problem or a mixture of both. If the fuselarge is twisted nothing will resolve the fault other than a rebuild and loads of dosh - a write off!
A factor of most high wing types like the Cessna is that the flap when lowered lowers into the propellor wash ( which is predominately portside) deflecting this turbilent air outwards causing an early wing tip stall and making the port alieron stall without it reaching it's critical angle. Any addition of aileron will in this condition agravate causing a rapid increase in yaw followed by a rapid increase in the angle of bank beyond the flight test initial 20 degrees.
However if the large wing drop is only present with say a typical approach RPM of 1700 then what I have described is the case. A pitch forward will unstall the wing very quickly and you will not experience the same phenomena. Rudder only sufficient to prevent further yaw, ailerons only when the wing is unstalled.