Various embodiments include a system having: at least one computing device configured to tune a set of gas turbines (GTs) by performing actions including: commanding each GT in the set of GTs to a base load level, based upon a measured ambient condition for each GT; commanding each GT in the set of GTs to adjust a respective output to match a nominal mega-watt power output value, and subsequently measuring an actual fuel flow value for each GT; adjusting an operating condition of each GT in the set of GTs based upon a difference between the respective measured actual fuel flow value and a nominal fuel flow value at the ambient condition; commanding each GT in the set of GTs to a part load level, the part load level representing a fraction of the base load level, and subsequently measuring an actual fuel flow value for each GT at the part load level; and calibrating the set of GTs based upon a difference between the measured actual fuel flow value at the part load level and the measured actual fuel flow value after adjusting the output to match the nominal mega-watt power output value.