Brain waves: what distribution of amplitudes is correct?

Question

IT education

Greetings!
Who has experienced band power (amplitudes) of brain waves? I can't find a clear source of which wave has the highest amplitude, which one is next, and so on.
At the input: raw EEG (encephalogram) from a single-electrode device (I don’t have one, they sent me already uploaded CSV), point FP1, sampling frequency 100Hz.
What I do: I take 2 seconds of the signal, I do FFT (AForge library), after applying the Hamming window before that. It turns out the spectrum. Then this 2 second window moves, and at each moment in time I have a spectrum for the last 2 seconds.
I worked with the spectrum many times (for sound, different signals), there are no particular questions here. But the result is discouraging. In general, the picture of the spectrum is similar to the truth (in different articles), but the amplitudes are strange. Those. what I do next: I break the entire working range (0.5-50Hz) into pieces, in accordance with the wave ranges (Beta, Theta, ...). I consider (using the trapezoid method) the area under the curve. I normalize to percentages. In the first place is Delta (this is logical), and in the second, sometimes going to the first - Beta. I can't figure out if this is correct or not. On the one hand, Beta has a wide range, on the other hand, the curve is usually close to zero at these frequencies.
Here's what I get:
https://gyazo.com/8a47503554d266cd927eb2108376509e
The customer claims that alpha > beta and delta > beta (as it should be).
I would be grateful for help.
UPD, first of all, I would like to understand: in my spectra, Alpha always has the lowest spectral density. Looks like he should be in second place. What could be wrong?