According to your figures your ratio would be 90% if you loaded the caravan to its maximum upgraded MTPLM. The 85% is guidance not a fixed limit and its introduction is shrouded in mystery.
Other things affecting stability are things like car suspension, tyre pressures on car and van, where loads are placed, noseweight, does car have trailer stability mode, driving speed, road perturbation, weather, effects if other vehicles etc.
With your car I would be happy to drive the outfit fully loaded. But why not start at a lightly loaded caravan and get a feel for your outfit, then as confidence grows you could increase loading.