They are somewhat fixed. Try to enter e.g. wishing well garden as early as possible and simply smash the chest. The resulting loot is (as of actual patch and taken from memory) around level 10, while you can find the entry with a level 5 party. It will still be level 10 if you enter the complete map (Hiberheim) much later.
Same is true for e.g. the chests in and around Hunters Edge. I often have a level 17/18 party there, chests seem to be fixed to the assumption of a level 16 party (which would be roughly the standard non maximized level on normal difficulty).
Regards,
Thorsten
Last edited by Thorsten; 03/12/14 09:22 AM.