Frequency vector of the pwelch?

Hello,

I have an EMG data and I am using pwelch to resolve the frequency spectrum. I have divided my data into individual active zones of different lengths.

[pxx2,F2] = pwelch(activezone2,[],[],[],Fs,'power');

plot(F2,10*log10(pxx2),'r')

powmax2 = max(pxx2)

[~,idxMax2] = max(pxx2)

FreqMax2 = F2(idxMax2)

Pdist2 = cumsum(pxx2);

upperidx2 = find(Pdist2>=Pdist2(end)/2,1,'first')

loweridx2 = find(Pdist2<=Pdist2(end)/2,1,'last')

MidFreq2 = (F2(upperidx2)+F2(loweridx2))/2

and I repeat the same for active zone 3, the values which I am getting for power is different but both the zones are genrating same frequency vector. As a result median frequency is coming out to be the same for different active zones.

I have tried it with different window size, overlap and nfft but the F2 vector doesnt change.

Can somebody guide me on this topic? Thanks..!!