That's completely at odds with what Cessna Wichita have to say, if the temperature is greater than depicted on the chart for the specific altitude you may calculate the density altitude then use the temperature and altitude which will give the same density altitude. The example I used when I communicated with them was for a C404 take off distance at sea level on a 50°C day which gives a DA of 4,200, but the chart only goes to 40°C. Going to 40°C and pressure altitude of 1,000 gives a DA of 4,238, they deemed that an acceptable technique. Aircraft and engine performance is all about density altitude.