Random number for complex number

My task is to simulate a greedy algorithm which is used to find best subcarrier response and estimate capacity of whole channel.

ht=complex(normrnd(mean_R,sd,[K M]), normrnd(mean_R,sd,[K M]));
hf=(fft(ht));

This part is used to produce response matrix with K user and M sub carrier and transfer into frequency domain.

UFG=[]; UFG=sort(hf,'descend'); UFG=(UFG(1,:))'; These codes are used to find number with max magnitude in each column

C1=[C1 mean(log2(1+(abs(UFG).^2)*SNR_Value))]; This code is to estimate the capacity of subcarrier. So the graph of Capacity should be a log function

The final result is :

It doesn't match my estimate. I find for max complex number in each column in that matrix, it's magnitude produced when K=1 are always larger than K=2 and K=3. Is there some thing wrong in my codes?