Creating the proper Vref for a thermistor
Calculate or lookup the NTC's resistance for the highest expected temperature, for instance 40 °C. Let's say your NTC's \$\beta\$ is 4310, then the resistance at 40°C will be 5 k&Omega;. Now remove R1 and R2, so that you're left with a simple divider NTC/R3. The 5 k&Omega; is your lowest resistance, and will give you the highest output voltage. That's your 1.6 V. Then

\$ \dfrac{R3}{R3 + 5 k\Omega} \cdot 3.3V = 1.6 V \$

from which you can calculate R3 = 4.7 k&Omega;. At 40 °C the output will be 1.6 V, decreasing with lower temperatures, like 1.06 V at 25 °C. As you can see the curve is fairly linear: