The Falcon is an impressive model although I have no interest in BR diesels and despite the earlier reservations.
On the latter, I believe Adrian hit the nail on the head about the camera angle. A lot of the prototype photographs were probably taken using the then standard 50mm lens and the camera at any height from 1.5m to 2m above ground or platform level.
The model photographs, I suspect, are taken on digital cameras possibly using the macro setting to get as close as possible. These are generally taken from an elevated position which would work out as if we were standing about 1m off the ground placing the camera about 2.5m to 3m off the ground thereby creating a different camera angle.
I have noticed when I have taken photographs using my digital camera on macro settings distortion creeps in to give a slight fish-eye effect.
IMHO the only way to obtain a visual prototype/model comparison (other than engineering drawings) is to photograph the model, using a 50mm lens, as close as possible to the angle as in a prototype photograph.
Not having seen the real locomotive, model or drawings and not being my interest, I wouldn't know about any inaccuracies.