Folks,
Boeing publish "Optimum Cruising Level for Short Sectors" ( or a name to that meaning) and is designed to give minimum block fuel burn on short sectors.
Compared to common airline flight planning practice, the numbers are quite interesting, producing relatively low levels.
On Australia east coast sectors, I regularly used to operated at said levels (as opposed to as flight planned) passenger comfort permitting, and always beat the plan.
Generally as long as TOPC is before TOPD, its good - a slingshot flight.
The old "theory" but never was correct, even for straight turbo-jets, and progressively became less "right" as by-pass ratio increased.
Tootle pip!!