Either formula works, the overhang is 76" btw. From camper front bumper at bulkhead to 2017 GMC axle is 53", the bumper corresponds to the front jack location. For reference the OEM gooseneck ball is installed 2.75" ahead of the axle centerline.
Bigfoot plaque says with propane (40#), water (312#), fridge (?), camper should weigh 3220# with the COG 55" from the front bumper or jack bracket.
Using above posted figures and weight of empty camper with battery is 3674#, COG comes out to 60.29" from front bumper.
My scales with what the camper plaque stipulates will weigh 3936# with COG 54.5" from front bumper.
With what the plaque stipulates in addition to generator and battery, weight is 4083# with COG 57.5" from front bumper.
So COG does move around a bit. Weight in the rear such as generator and battery have quite a bit of effect. As one estimated, pulling almost 300# off the front axle is doable.
This is a no frills unit btw with just dually camper jacks, a/c, and gen ready adding to the weight.