Well any Icelander will tell you that is a crock of shit...
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or any farmer....
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Don't know if you read the article, but it's correct that the flotation is determined by the size of the contact patch, and the contact patch is determined by the tire pressure, not the tire dimensions (at least directly). In extreme cases, like comparing a tractor to a Jeep, the disparity in vehicle weight is so large that yes, it would be impossible to support a tractor on a Jeep tire, but even if you could, the pressure required in the Jeep tire would be massive and would never be able to achieve the same contact patch as the tractor tire. But in comparing 10.5 vs 12.5 wide 33" tires, the weight bearing capacity of the tires being compared is close enough that it's not a factor limiting what you can air down to, with the possibe caveat that without beadlocks, on the same wheel width, it may be that a 10.5" can't air down as far without risking losing the bead.
But...if you took both tires, at the same pressure, the flotation would be equal.