RNAi efficiency in different tissues

Does anyone know if RNAi works equaly efficiently in all tissues in N2 worms (I know neurons are resistant to RNAi) ?I was recently testing RNAi for my gene of interest in N2 worm and did not see any phenotype. However, when I did the knockdown in hypodermal specific RNAi strain, it showed the phenotype.Could this mean that in wild type, sufficient knockdown is not achieved in hypodermis?