I can't help feeling that this thread is getting bogged down discussing percentages rather than the getting to the crux of the matter that is how much nose weight is required to achieve a good tow. There is no fixed or definitive solution to this so; Keeping full regard of the law and the technical limits set by the manufacturers, you only need as much nose load that allow you to keep in full control of the outfit.
BUT
As so often happens, focusing on a single criteria you can loose sight of the wood for the trees, there is a bigger picture, and nose load is only a part of it. In my view there are five major influences that determine how well an outfit behaves on the road.
1 Mechanical condition of the tug and trailer - especially suspension and tyres
2 Relative weights of tug and trailer, not the theoretical towing ratio, but the real life ratio. The trailer should be kept as light as possible.
3 The way tug and trailer have load distributed in each vehicle (this produces the nose and axle loads)
4 Road conditions.
5 last but not least, the drivers driving style and competence, especially speed.
Fundamentally instability is created by excessive speed, (not necessarily the same as speeding) so if you outfit feels less than fully controlled slow down, stop at the nearest safe place, and readjust the loading to see if it can be improved.