I'm inclined to agree with RJR above that the cab was located ahead of the firebox to improve visibility. I also have to wonder if part of the thought that went into Camelback engines was related to both vertical (as noted above) and horizontal clearances, wheel base and curvature.
How at all would "visibility" be impacted? And how does cab placement have anything at all to do with wheelbase? In point of fact, the "visibility" of the crew was terribly curtailed with this design, since, without a fireman in the cab, the engineer was virtually blind when going around left-hand curves.
As can be seen below, the firebox is as wide or wider than the cab itself. You can't place the cab in the "normal" position because there would be absolutely no room for the crew; placing the cab "behind" the boiler also makes no sense; and placing it high enough over the firebox so that there was room for the crew would place it too high.
