help needed to understand the output

I am trying to interpret the FFT output in the array Please let
me know if my interpretation of the data below is wrong or not

If I set the RFX2400 tuned to frequency 2.4G and the FFT size (fft_size)
is set at 256 and the decimation rate (decim_rate) is set at 8 then the
value at the array index is a square magnitude value of the signal at

freq(index) = 2.4G + (64e6*index)/(fft_size * decim_rate)

Am I wrong in my assumption?