Was at some time on 747 classics (rolls royce engines) a reccomendataion or requirements to motor the engine until egt had decreased to below 150 and we also had this on the 737 300/400 models for a while. Ex engineers turned pilots would also say that the worst thing to do to an engine is to let it peak and then make adjustments so they might move the start lever to idle at 25 % because the momentum of the start was happening and the acceleration would continue rather than wait for a peak and then add fuel which might begin another acceleration ie engine load. That kind of thinking is similar to the stable thrust requirement of 40% before setting take off thrust. The stability of the engines is more important than the amount of thrust. That is you wouldnt set say 50% then pull them back to 40 and then hit the toga buttons for takeoff as that would be an up down in thrust and engine wear/load which is pointless. What you are seeing in your captains is a reflection and variety of past experiences, past SOPS which are broadly within the requirement to not put fuel in too early, and dont let them burn at the top end of the start, dont run starters for longer than 2 mins. Ask them the question about their actions and they should have a story or 2 for you which will make the sops and individual actions stick in your mind for the understanding you have gained
