thanks for your reply, Gary.
I fully understand the new price system and I checked that for example in UK and the Netherlands it is possible to obtain 20% as Diamond and 15% as Platin. However, it has never been the case in Germany and I am wondering why.
It is actually quite easy to see when you book a car in Germany.
The standard rate has obviously no discount. then platin has W2U and Diamond has W3U. in 5% steps that means, 10% for platin, and 15% for Diamond.
but at least some time or station in the future it should be possible to get W4U as Diamond and W3U as platin.