The cupola should be entirely in front of the rear side window. Weaver (in O) and Precision Scale (in HO) made the same mistake on their brass N6b in having the rear of the cupola over the window instead of in front of it. Straight-on side shots of the prototype are not common, but here is one:
https://encrypted-tbn0.gstatic...TU1ZeDA&usqp=CAU