as you can where you burn the least amount of fuel and then idle descent.
I think the main thing isn’t so much the fan as much as it is the airplanes are just so well designed. They’re “clean” meaning they produce very little drag.
Even in a 737 you have to be careful not to get caught high otherwise it’s really hard to come down and maintain speed and still make your altitude restrictions.
Those big engines are definitely impressive though.