It would be best if it were, but sometimes it nost possible with parabolic reflectors of MH. So if you
"need" the light then it would be best to try to fit it on the relector. But for my tank, the MH is more than enough light, so my PCs are just for actinic color. And my reflector does block some of my PCs, but not a bg deal. I rather have the PCs blocked than having the PCs block some of the light from the MH.