My 61" Husky was set up at the dealer with ~15psi in the rears per sidewall & OM. (ouch ouch ouch etc ... &$#@*% moles) 12 psi was a bit stiff too so I went down to 10. That works best on the Dixon 4228, too.
8 psi would be my low limit as a two psi drop might have a tire slip off the rim, and if adding tubes they'll scrub/wear inside a tire at 6psi or so. (BTDT)
btw, first edition of raising the seat (I'm 6' 2") was with wood blocks and I'm thinking of re-working that to include more springs. (&$#@*% moles ...) Haven't had an L5 disc for decades and I have to sit up straight vs using the backrest when mowing. (Big help there.) Armrests came off the Husky after one mowing, and that helped me find the best posture for the job. (~2 ac)