When you restore 100% of front axle weight to unhitched weight, most people on here report about 20% goes to TT axles. But Ford recommends only restoring half of the lost weight on 2011+ F150s, so the 12% seems more realistic. So that means you effectively have an additional 12-20% of TW available as payload.
Honestly, I would not worry about 100-200 pounds. The truck should handle well at GVWR, slightly over even. If you are the type of person who is going to wprry about that kind of weight, get a bigger truck.