The figures you are quoting above are likely according to a standard measurement that does not block rearward visibility at all, in other words, below the beltline, or cargo cover (approximately).

That is why the 5 touring is shown to be the same as the 5 sedan.

Now, I don't know about carrying fridges, but I do find the cargo area above the beltline to be handy in the X5, X3, and 5 touring, as Trainer says. That may not be true for everyone, but to me, the X6 has less useful space than the other SUV/SAV/Touring models, because of the slope of the rear window. If a 5 sedan (plus 10%) has sufficient luggage capacity for you, then the X6 should be just fine (I have a 5 sedan, and it actually has a very useful trunk, just not the same as an SUV or touring model)

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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