Vass should make new last for F, U and other modern last with more narrow heel for export.
We start thread on Vass heel width and send to Eva Vass,
Thanks for the answers, guys. The heel slipping is new to me, I've never had this with any of my shoes. I don't think I have a particularly narrow heel.
I suppose the problem comes from the shoe being too long for me. I hope that U last 41.5 will solve this problem.
And thanks for the hint with the downsizing for the F last. I will keep this in mind. ATM I think it's best to find out my size with the U last before switching last and starting the trial and error process again.