Clearly, you would need detailed performance tables for the aircraft in order to answer WindTunnel's question. For starters, is there a holding table giving fuel flow at various altitudes based on weight of aircraft?
Secondly, is this table at the minimum fuel flow necessary to sustain flight at that altitude? If the answer is yes, then you have the solution to WindTunnel's question.
The general solution is for the aircraft to be nearly at its maximum altitude. This is because the engines would be required to operate at high power settings where the thrust produced per lb of fuel consumed will be greater than that at low altitudes and low power settings. Holding tables often demonstrate this, with lower fuel flow's at the higher altitudes