There's a small change to the tailgate on my 2018 F150 that for some reason I hadn't noticed until now: There's more clearance when the tailgate is down.
On my 2015, same truck, same bed length, same suspension, same stinger, you could not drop the tailgate all the way, but had to rest it about halfway down the power jack post. On the new one it clears just fine.
I've no idea why it clears now. The tailgate appears to be just as tall as the previous one, and the hinges are no different. Perhaps it's just barely shorter, not enough to notice visually?
I guess my plans for an extended stinger are no longer necessary.