"The ETRTO also states that where CP tyres are used on the rear axle
(single fitment), they must be inflated to a pressure of 5.5 bar instead
of the normal pressure of 4.75 bar for example.
l MICHELIN CP marked tyres are therefore specially designed to be driven
at an inflation pressure of 5.5 bar (550 kPa) This higher pressure improves
road holding and increases resistance to the challenging driving and usage
conditions encountered by motorhomes, especially with regard to loads
(occasional static and/or dynamic overload associated with this type of vehicle;
considerable rear overhang, load imbalance, high centre of gravity due to
highly positioned loads) and long-term periods of disuse."
In general inflation is related to load and tyre size, with a tag axle and under max load I think 79psi will be horrible.
You can contact your tyre manufacturer for technical advise.