Step climb is a pilot imput, and it will be performed at a waypoint (geographical step) however the FMS2 has the capability to compute an optimized point (lat and long coordinate) from which it would be better to climb to the specified step climb flight level.
It takes into consideration the aircraft weight (power available, power required stuff
) in order to minimize fuel burn during the climb (at max cruise thrust) to the desired step flight level along with the fuel flow(step TOC weight)/forcast wind.
All this has nothing to do with the optimum flight level, it is the optimization of the climb to a step altitude.
Step climb/descent can be an operational requirement (ATC Notams etc...) and will all know that there is no savings in that case, so the FMS will try through optimization of the step save some nickels, weithereas optimum cruise flight level will save more dollars