Partly unsupported tread does not refer to the entire tread being off the ground. That would be a fully unsupported tread.
It refers to a portion of the tire not being fully on a leveling block.
Tire hanging in the air, no problem for the tire.
I find the rig is more stable if the jacks take most of the weight but the tires are still on the ground or leveling blocks to some extent. Tires on the ground adds some friction which seems to take that side to side sway that I notice when both fronts are fully in the air.
As others have said. never raise your back tires or you might roll away.