My 5" 629-3 Classic DX has the raised portions of the front of the cylinder beveled and my 6.5" 629-4 Classic has both the raised and fluted portions beveled. Although I don't know if it shows well enough to see, here is a photo of those two guns along with a 6" 629-1 that has no beveling.
It seems to be a common feature of the -4s and perhaps to some extent the -3s.