I don't doubt you measured 4" someplace Roy. But my Cat 2 PEC measures 4" from the center of the swivel ball pin to the center of the implement lift pin. So if a Cat 2 is extended 4", it stands to reason that a Cat 1 would be less than 4" - by virtue of the smaller Cat 1 hook size and lift pin diameter.
That said, I've never actually measured a Cat 1 myself - I'm just repeating that 2-3/4" measurement posted by another Cat 1 PEC owner last year. Perhaps there's been a design change at Greenwell since that measurement, and/or since my Cat 2 was purchased.
//greg//