Mike,
I don't know how you collect your data. I have EasyWeather logging all data from my weather station. By comparing the log of "Heat Index" with the display of BIT I see the following.
Actual weather station always shows correct value. Logs from EasyWeather also show the same value as the display. BIT fails to show the heat index value as soon as the number becomes a 3 digit number. BIT shows N/A in this condition.
I don't know of any other way to explain this. Everything points to BIT being at fault.
Don