How to strengthen a press brake die

I use my HF 20T H press as a press brake with a homemade die. I'm trying to put a fairly sharp 90 deg bend in a 20" piece of 16 ga mild steel and I'm getting too much deflection in the ends of the die. The bend isn't completed because of this. There's about 3" of stock that doesn't have enough bend.

Here is the die, front view & cross section:

Do you think that this will be enough? Would a flange on top of the wing add significantly?

Thanks, Bob