[Q] [RAY] Antenna problem topic

Well, my mobile network worked fine until 6 months ago when i experienced HUGE signal loss.
few weeks before that i had my phone's display being replaced because of minor damage + unlock problem
Now, i ave a simple question:
My friend has the same phone and he has the cover on the metal part (arrow position on image), while I dont have it.

I have tried:
1) Different SIM cards (no result)
2) Different ROM-s (original and custom, no results)


Could this be the cause of the low signal problem?

Thanks in advance.

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