Nope I have near used the Fuel and Payload loader before.
If you haven't use that panel before, doesn't automatically mean that, if you use the PMDG FMC to set the load, the actual simulated parameters aren't the same.
An easy way to verify if this is the case, would be checking the payload values in the default loader BEFORE and AFTER changing the stations load in the PMDG FMC. If they change, it means PMDG is using the standard stations, if they don't, it means they use their own internal simulation.
Could this be a suggestion for the next update, to have GSX board passengers according to the PMDG FMC ?
We made an universal add-on that works with FSX. We didn't do an add-on for a PMDG airplane. If a developer takes the route of simulating a system that exists in FSX, but in his own way, it should be prepared to accept the risk that doing this would cause issues for users of other add-ons that makes calculations based on the standard system.
Such values might be used by many other add-ons other than GSX, like flight planners, etc. It's just wrong that *all* of them would need to adapt to an airplane that used a non-standard system, the proper way would be the airplane developer would write back their own internal values into the standard places, to maintain compatibility with everything else, not the other way around.