Raynox DCR-1850PRO Question - Camera max zoom 6X

[Gil ab ca]

Does anyone have any idea why the RAYNOX DCR-1850PRO (1.85x lens), cannot be used for a point/shoot camera with more than a 6x zoom? I have a Kodak DX 7590 and a Panasonic FZ20, and have one of these lenses. From what I can see the pictures at the higher zoom settings ( 10x - 12X) look great. They actually look similar to the Raynox DCR-2020Pro that I also use.
Thanks
Gil