How do i set "volume" limits?

Hi, Using the latest freeradius&dialupadmin on debian. I did find the option to set time limits (day,week,month), but i 'd like to know how i can set volume limits. (MiB's up/down transfered) The up-/down transferred MiB's are sent by the NAS and stored into the db. I can see all users sessions up/down MiB's tranfered if i query them in the accounting tab of dialupadmin. Though i can't see anything in the "user statistics" of any of my test users. The page just stays empty when i hit "show", strange. Can anyone tell me how to set daily/weekly/monthly volume limits? Many tnx Yves