calculate power spectrum from complex number in simulink's spectrum analyser

In my example of N=8, X(1) = -1.92 -0.8i X(1) = 2.08 X(1)/N = 0.26 POWER (w) = X(1)^2/N^2 = 0.0676 w = 30 + (10*log(0.0676)) = 18.3 dBm

Reading in spectrum analyser in Simulink is 23.979 dBm for double sided spectrum and 26.99 dBm for single sided.