The new 42 back and lugs are even. I’ll check the Perpetual Blue later today.
The new 42 thickness is 13.8 mm. The full size Perpetual Blue IW503203 is 15.5 mm. The new Perpetual Blue IW503401 thickness is 14.9 mm.
That may explain the appearance of the delta. My older Perpetual Blue is 15.5 mm vs 13.8 mm (Delta 1.7 mm).