If your trailer is level and it's 17" from the ground to the coupler, that's what it is??
I've got my hitch head set on the lowest hole on my drop shank and my trailer sits level at 18".
This is my old F150, but I used the same hitch setup with my new F150 and this is where it works the best for me.
If your truck is taller, then you need more drop on the hitch.
Or you need to lift the trailer axles to get closer to your lowest hitch setting.
Good luck!
Mitch
2013 F150 XLT 4x4 SuperCab Max Tow Egoboost 3.73 gears #7700 GVWR #1920 payload. 2019 Rockwood Mini Lite 2511S.