I know you said you had all size bg in the pond, but are you sure you have enough bg in the right size range to get the bass pass the 14" range? In my 2 ponds I have seen lots of small bg (2" range) and lots of trophy bg, but very few in between. My goal has always been trophy bg, but i rarely see any mid size bg.
Did your electro survey produce lots of 4-6" bg?