4s mirror back plates kills wifi signal?

Hallo, i have a problem , i tryed to change back plates from my black stock apple back, to one of those silver mirror type, i did a color conversion and it all worked fine exept when i installed the silver back plate i get vey bad wifi, i also have a gold coversion kit, just to see if it would be the same i tryed putting on the gold mirror back and again get very bad wifi, it does work but the speed is very unstable and the ange limitet compared to with my stock black back plate??? I also tryed a red one and it seemed to work without any problems, so it seems the problens is with the morror versions??

Any ideas and solutuons to a fix???