My own 6G Edge light and filter modifications are somewhere in the official Edge thread. Getting light across the front substrate, into the corners, and onto the front of the fish rather than on their backsides certainly wasn't easy.
I suppose the 12G makes it much easier though. For the height should allow an adequate spread, and you should be able to aim enough of the light at the front pane for it to reflect off the front pane and back onto the front of the fish in order to actually visibly illuminate their colors and iridescence instead of just washing them out.
I'll have to think about whether that is adequate still, for maybe I'd be better off just doing my own custom tank from scratch where I could mount a bar of LED's on the front inside edge of the tank anyway. $100 isn't bad in any case, though perhaps I'd have to include the price of a Dremel as well.