Will coffee in two differant size styrofoam cups in the same room conditions cool at the same rate? One cup is 8 oz. and the other would be 12 oz.
If we may assume that the cups have the same form factor, or that the cups are identical and that the 12 oz just fills it up farther; in either case the 12 oz. will stay warmer longer.
Agreed with Georg: that the dominant heat loss mechanism in this case will be evaporative cooling