mfilt.firdecim function not visible on Magnitude Response

Hello, I'm quite new to Matlab. I'm trying to model a digital filter followed by a decimator. I've written:

num_fir1 = [1 4 6 4 1];
Hfir1 = dfilt.df1(num_fir1, 1);
Hdecim1 = mfilt.firdecim(2,num_fir1);
fvtool(Hdecim1,Hfir1)

I don't understand why the 2 filters Hdecim1, Hfir1 looks identical. I was expecting to see the aliasing effect on Hdecim1.

Thanks.