Thanks for the comments.
The strap pin on the other side of the omega cut was already there when I purchased the basses (serie 1 and 2) therefore I do not know if it's originally like this on these models.
The serie 2 is a 32 and the serie 1 and 20th anniversary are 34.
As I'm only 1,8M tall and I might admit that you should get used to the 34 bass, I purchased double strap from GruvGear (
http://www.gruvgear.com/duostrap) and now I do not have any more problem with back ach and the basses are well balanced !
Thanks again for your comments.
Franck