For those interested – required reading on the Leader Class starts with a good general account in "Bulleid – Last Giant of Steam" by Sean Day-Lewis, a very readable biography. More information, and perhaps more technical detail in "Bulleid of the Southern" by H.A.V. Bulleid, the great man's son and also an engineer.
Then there are several editions of Kevin Robertson's "Leader – Steam's Last Chance" which is a comprehensive account with many interesting photos, especially of the construction phase. Robertson's research is very good but perhaps understandably, he does not have the technical knowledge to analyse the subject in depth. .
See also – "Bulleid and the Turf Burner" by Ernie Shepherd which details the "Irish Leader" which is a subject in itself, and seems to have worked rather better.