I was lost as well. Don't use the supplied mount with the grill, It does not connect to the bumper mount. It is for table mounting or to be mounted on the side of a trailer for those that do not have a bumper mount. on the base of the grill you will see both horizontal and vertical tubes. The bumper mount has two vertical rods, these rods will slide into the grill base vertical tubes when lined up properly.
I hope this helps you. It took me at least 30 min of scratching my head trying to figure out how the supplied base hooked up to the bumper swing mount. They really need better directions
Jason & Wendy
2014 Ford F-350 Lariat 6.7L PSD
2015 Keystone Montana 3711FL
B&W Patriot 16K Fifth Wheel Hitch