Default values in selection screen of reports

Hi,

When i'm opening certain report transactions (say ME5A), some of the selection screen fields including dynamic selections is populated with default values. Is there any settings to fix default values for the selection screen (other than variants) ? Also, is there any way to set a variant as default ? How to get the selection screen clean & empty without user default values (i.e except the system ones) ?.

Thanks in advance.

Sheeja.