Hi,
unfortunately I did not take pictures of the last time we successfully (and with the rear seat bench FULLY usable) transported a set of 22" tires in our 5-seater MX, over a 400 mile drive - but I assure you that the method described above IS feasible, for ALL versions. In the older 7-seat, and current and older 6-seat versions you will not have very much rear visibility, thus my recommendation to put the slightly smaller front tire/wheel in the middle, flanked by two rear tires/wheels.
On May 9 we'll drive to the Service Center in Düsseldorf, Germany (± 320 miles roundtrip) to have our 22" referral wheels fitted - outbound with a set of 22" tires in the rear cargo area, and homebound, in addition to this, with a complete set of 20" winter wheels on the flat-folded 2nd row seats. And yes, we will upload photos of both configurations!!
To those of you who might wonder why all this transporting tires around - no, we're not trying to beat YouTuber "Teslabjørn", but after successfully bidding for one of the 22" referral wheel sets in January, we bought a second set of new (but late 2015 vintage) 22" tires at a ridiculously low price (± 200 $) a month ago, and want to put those to use first (the new "referral" tires are not yet mounted on the rims), and then use the "referral" tires once the older ones are done.
And tire or service centers generally have no idea of how to fit tires efficiently - they just kind of throw them in. We experienced this both with our MS, and now with the MX - with the latter they even claimed the wheels would not fit in the vehicle, and consequently sent a Mercedes Sprinter van to deliver.....