We substituted MARCS atmosphere models for ATLAS models in our analysis procedure and compared the [M/H] values for a sample of stars between 5500 and 5000 K. There is an increasing offset in [M/H] using the different model atmospheres that corresponds to the trend we see in the mean raw [M/H] for our high-S/N sample (black dashed line for reference). In this temperature range, the mean raw [M/H] values of our sample as a whole decrease by about 0.15 dex, so the change in atmosphere models alone corrects for more than half the trend we see.