In Davis's BTZS he writes about a normal contrast of 0,5 which I used in the beginning and got flat negatives. He talks about an average flare of 0,02 which I based my exposure on.
I quickly moved back to a "normal contrast of .57 and got better results like the time before I tried out BTZS. This confused me for a long time.
Then I read a few things from Stephen Beskins (a lot I still do not understand), explaining a bit more about flare.
As I understand it the flare mostly showed by BTZS is just too small. At least the way I understood it.
Although flare is discussed, the dominant usage of such a small amount of flare made me use too small a amount.