Using WS-FTP, valid user can't go into folders they create
 

I have some users, all of which belong to the same group. When they log into the server using WS-FTP they are jailed into a specific directory. A user can create a directory but he can't go into that folder (nor put anything into that directory) , even if he is the one that created it. The permissions are automaticaly set to 755. I have to change the permissions of that folder (as root user) so that the permissions are 775. Is there a way to have any folder created in that jail direcotry default to 775? And if not, what setting do I have to change so that users can create and access those folders?

I am using wu-2.6.0 and linux kernel 2.4.18

Thanks for your help