Jaeger-LeCoultre Master Ultra-Thin Perpetual stainless steel has a diameter of 39mm, a tad bit bigger than the previous version they made in the late 1990s and early 2000s with a 37mm case. You can debate about the size of these ultra-thin dress watches, but in the end I am convinced that 39mm is a very acceptable size for a mens dress replica watch.
The former Master Perpetual (reference 140.8.80 S) and the new Jaeger-LeCoultre Master Ultra-Thin Perpetual Replica I am talking about here (reference 1308470) have a dial lay-out that has been rotated 180 degrees. In the former 37mm version of this stainless steel perpetual calendar, Jaeger-LeCoultre used their caliber 889 movement.
The current 39mm version has JLC caliber 868, that consists of 336 parts and only measures 4.72mm in height. The case of the watch is 9.2mm thick and has sapphire crystals on both sides.