Sorry to tell you but this is a luck of a draw, some cards can unlock to 20PP, some can even unlock abit more, but its simply rated to be 16PP, and some can't unlock at all, like yours I guess, if you disbelieve me see this page:
http://www.leadtek.com.tw/eng/3d_graphic/specification.asp?pronameid=249&lineid=1&act=2
-Jo.
http://www.leadtek.com.tw/eng/3d_graphic/specification.asp?pronameid=249&lineid=1&act=2
Written on Leadteks site
Pixels per clock (peak) 16
-Jo.