KW, That does not compute:
In the example shown in post, the area load with floor spreaders is 1.2x0.5,
In the OP example, the floor spreader load is 1.5x3=4.5, 2000/4.5=444.44
Note that area calc for a contact load with spreaders is the same as UDL.
JT,
With heavier loads, especially irregular shapes, you must look at the CG of the load. The resultant force, when the aircraft rotates or banks is very important. Restraints, depending on the angle of restraint, size, shape, or where the object is located, may not be able adequately distribute the load to the floor uniformly. The spreaders must be designed not to flex and create a punching shear or excessive bending moment in the floor. Max angle on a strap is 30 degrees, so a high CG of the load is going make things difficult. Straps are not infinitely rigid, so any flex redistributes the load to others.
Bank the ac 25 degrees, and that offset cg load will distribute unevenly to the spreaders, and any flex in the spreader will create a concentrated load.
In general, this is addressed in the Load Factors and Apparent Weight calcs, and these are certainly oversimplified with a perfect center of mass. It is the unusual loads, especially the ones that are near floor limits, that should be addressed.