This response is courtesy of Martin Beriswill from Doyen Medipharm:

The determination of what pressure to test packages at is a calculation that provides you with the pressure parameters based on material and package size.  The pressure test is used to simulate the packages in high altitude conditions, either mountain area or and/or planes.  The pressure is used to confirm the materials and especially the seal strengths are sufficient to maintain the seal integrity and therefore the package sterility. Check with the supplier of the pressure testing equipment.  I would think they would have the calculation and could also provide them with more specific details.  Or contact me and I’ll try some other resources.