For my application, I plan on having two nRF24L01+ Modules communicating with each other. They will each be placed in plastic enclosures and need to communicate over no more than 3-4 meters with the potential for people to walk between the enclosures.
have you tried dropping data rate to 250kbps ?
i get about 15m through walls . which is pretty decent.
i haven't tried enclosing them as yet but i should imagine they would still work