For more flex, you loosen the nuts away the center - right for the top nut, left for the bottom nut, seen from behind. That said, I (weighing in at less than 160 in socks) felt the stock system was a good idea, but too stiff, as I found out after I had exchanged the black tongues for the softer red ones. So I switched to ACSS in my second season in the UPZs. Judging from the pic, you are already maxed out in terms of flex. Some very accomplished riders I know simply remove the forward lean system (the same for Deeluxe), but I feel safer having a spring in there, not sure if it makes any difference for my riding.
The bottom nut is 10 mm, I think. I can check over Xmas if you want.