Pressure cup is not a term I encountered when I was last searching for copper fittings, about ten years ago for a bathroom remodel. Is pressure cup a synonym for tapered thread which needs to be tightened, or does it refer to the depth of the solder section for residential and commercial water applications where the water from the mains is under pressure?
P.S. I have found a document that says it refers to a deeper solder depth, for pressurized systems.