Raspberry Pi Box and z-wave issue

I just had an interesting experience with raspberry pi boxes. I was running my system using a PI2 and for z-wave a razberry board housed in a clear plastic box. It all worked reasonably well.
I then switched to a PI3 I happened to have, mainly to create a backup system in case one goes down. I used the same razpberry board but in a black plastic enclosure. I found I had real problems getting z-wave reliability until I took the lid of the black box. It then all started working fine again. So if you are having issues with z-wave signal might I suggest checking your raspberry enclosure is not causing the problem.