If you look at the picture above your post, around the hitch ball, you will see the equalizing bars coming back from the hitch (not the electrical hookups, which are looped in the same location). They are under the trailer A-frame, and are about 3' long. Think of those bars like wheelbarrow handles. If you lift on them, you will raise the back of the vehicle, and transfer load to the front axle. Those bars are lifted by being connected to the front of the trailer, on the A-frame. They can swivel left/right, so the trailer can turn corners. But by tensioning them, pulling them upwards, load is transferred off the rear axle, to both the front axle and the trailer axle.

The X5 doesn't have 50-50 weight distribution except when it is empty. Putting a load in the back of it, or a heavy hitch load on it, changes it towards your 40-60 (F-R) number, although I don't know what the actual distribution would be. A weight distributing hitch helps shift it back closer to 50-50, although you won't likely get right to the empty weight distribution %.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue