That’s my point, at that low a pressure a direct vertical impact will be fine. But surely the tyres are more susceptible to folding over with pressures that low.
Big fat tyres still fold but not in the same way as a higher pressure smaller tyres, its much more progressive as opposed to the ‘collapse’ of folding a small tyre.
I hate tyre that collapse, to the point that even in CX races i run a little higher, but ive yet to have my fat bike tyres fold in quite the same dramatic way as smaller tyres. There is a case for slightly higher pressures when you can (i.e. with a sus fork) as the folding/rolling of the tyre on the rim can be felt and does require additional/different steering input (but the bikes steer differently anyway so not really a problem).