Replacing an iPhone 6 screen + proximity sensor issues

[andel]

To all the people out there experienced in replacing screens I have this ongoing problem that the proximity sensor is inoperative after a screen change on an iPhone 6. I've done about 8 screens so far and only 3 have worked correctly. If I remove the sensor from the screen and place my finger over the sensor it works so its not the sensor.
A quick google of the issue suggests the inferior paint quality on the replacement screen like back in the day of the iphone 4 or placing tape over the back of the speaker as too much light is getting in.
Can anyone add to this with things to try as I'm 100% sure it is positioned correctly?
cheers

[evilsatan]

If the sensor works when placing your finger over it then you know the flex is ok, if you are sure it is positioned correctly and the glass is clean then it must be to do with the panel. Can't say I've noticed this problem on any I have repaired, two glass panels have come unstuck from their frame though...

[Mobileman]

99.5% crap quality digitizer 0.5% you positioned it wrong as they do allow for a fair bit movement of its the proper glass they can be anywhere within sensor flex area and work fine.

Where you get the screens from ?

[Mobileman]

Hold the original and new up to the light and look at the difference in transparency you might be able to darken the new one using black tape on inside

[andel]

screens are from a supplier I collect from in Park Royal and they're quality is usually very good to be fair and a different supplier online. My suspicions were with the glass as I'm sure the flex is positioned correctly. I always make sure the contacts on the flex are touching the speaker contacts and the plastic spigots are through the flex and bracket with the whole assembly sitting down neatly. I'll try and do a comparison, thanks