You’re right, just one “try and see” is better than hundred theories 
Ah thanks; I’ve underestimated the MOQ’s of Chinese suppliers due to my European naivity 
Regarding your edit; your feeling can be prooved by simple math:
Note that your cup spring had an unloaded height of ~ 3,00 mm.
The material thickness is equal to ~ 1,7 mm.
On your axle stump with ~ 1,7 mm will the spring be flattened completely because its heigth was reduced for ~ 1,3 mm.
The spring was already totally overloaded and it reacted with a non-reversible deforming while loosing a good portion of its springiness.
With a cup spring like the given ones you need an actual axle stump length of about 2,7 or 2,8 mm.
(Without armour shim but an intact frame surface.)