Here's a little write up I did to help determine the right pressure for you:
Water down a flat paved area(driveway).
Pump the rears up to about 35psi.
Start riding the bike forward/reverse over the wet paved area letting small amounts of air out until you see a full tread width flat tire track left in the wet pavement.
Check the tire pressure in each rear tire.
Repeat this process w/the various way your trike will be loaded and record the pressures for future reference.
That's how I arrived @ 24psi left and 26 right for my normal settings.
Mines a Hannigan