Screen replacement (White area at top of screen)

Hello

I have now completed several iPhone 6 screen replacements however seem to get a similar issue on most of them.

When you turn the device on and the white Apple screen shows, you can see a slightly whiter patch at the top of the screen. This is near to the ear piece assembly area. I have taken apart again but I still seem to get the same thing.

I am sure it must be something to do with pressure on the LCD, but I just wanted to know if anyone else was suffering similar issues.

It is not a major issue as you cannot notice when using the device, but I want to know what i am doing wrong