Yes, it’s all very complex. I think it would be an acheivement if calculated values could approach those achieved on the road.
I forgot to mention the Gas Producer Combustion System (GPCS), if used.
A proportion of the exhaust steam is added to the combustion air. This reacts with hot coal to produce Hydrogen and Carbon Monoxide, which then burn back to carbon dioxode and steam in the combustion chamber.
This obviously reduces the blastpipe steam, but adds to the mass of the combustion gas flow.