Asset managers have to report risk ratios and to stay below limits. Sometimes, big 4 auditors are appointed to calculate those ratios.
One of them (no names here!) is using its "own" model to compute the risk you're taking on AT1/Coco bonds. 1/n
Every single client they have is "using" that model
File under what I call "illusion of science".
It's not because it has fancy equations that it's reliable or that you should not challenge it.
Same for "it has a big name on it"