I was fully expecting it to be 5 mm and although my measuring may not be that accurate it is certainly under 5 mm. I did notice from the movement picture that the movement is virtually flat to the watch case thickness and that the caseback is only very slightly raised whilst the glass is flat to the case. It really is not that much of a big deal at the end of the day as either way it is an Ultra Plate and IMHO a beautiful watch and I am happy. I have tried again to get better measurements and take some more pictures to try and show it more clearly. On the tape measure I have made sure the watch is dead on the 9cm mark and you can clearly see it doesn't reach the 9.5cm marker so IMHO is clearly under 5 mm and a fraction under the 3 mm marker.

watch on 9cm marker

watch under the 9.5 cm marker

Caseback depth and glass flat to case

Caseback depth and glass flat to case 2
Marc