thanks for this quick response.
I have ISPConfig 188.8.131.52, just isntalled it two days ago, but I cannot remember that I changed anything with the path-default.
If I add a new shell user, I do not change anything under "options", there I have for Dir the value "/var/www/clients/client2/web1"
If I try to change this to ...web1/./home/testerssh I get an error message "No ./ in path allowed".
Yesterday I tried "/var/www/clients/client2/web1/web" but then the jail was also created inside the web directory (as I expected).
I think there ist a config-file where I should change the path value. Can you help?