It wouldn’t surprise me if those of us running short stems like my 35mm are typically putting >60% of our weight through the rear wheel, so we should be putting >10% extra pressure in the rear tyre to compensate… Especially those of us that weigh north of 80Kg when kitted out to ride!
When I run my 4.0 JJs on solely tarmac rides, I typically run ~25/28PSI, but this hasn’t happened that often since getting my FatNotfat 29er wheelset.
On rides that include some off-road, I’ll drop the JJ pressures to ~18/20PSI if it’s been raining heavily, because the ride will still include ~5+ miles minimum of tarmac riding to get there and back.