Re: As for Shay's 1933.........

It is much easier to maintain stable water levels in a wagon top or extended wagon top boiler when ascending and descending steep grades than with a straight top boiler. With a straight top boiler proper water levels for ascending 7% grades can easily result in dry crown sheets or working water through the throttle on decscending 7% grades. Because the barrel diameter ahead of the firebox is of a much smaller size on a wagon top boiler it is usually completely or nearly completely full of water whether the locomotive is level ascending or descending. The switchback at Roaring Camp demonstrates this principle quite clearly.
On another point I agree with Earl regarding hooking up locomotives to get the best performance. In most cases run as high in the quadrant as possible without either losing power or going lame. As on old friend of mine form Britian used to say "use the steam expansively not extensively". Less steam used, less cold water put in the boiler, less coal or oil burned, less smoke, less wear and tear.
While at White Pass the #40's johnson bar required frequent adjustment when running from Bennett to Log Cabin. This made the difference between making it to the top in good shape or having to stop to blow up steam and build water before topping the grade.
If a locomotive is not "square", that is to say if the opening and closing of the valve ports is not even the locomotive will have at least one weak power stroke each revolution at short cut offs (hooked up). When this happens the engines lopes or surges and pounds badly. Under those conditions it is necessary to use longer cut offs (running farther down in the corner) just to keep from damaging the machinery.
When drifting or descending with slide valves we generally put the johnson bar in the corner to help keep the valve seats flat.