I have undertaken some measurements of RSSI (received signal strength) using an ESP8266 and an e-paper display that is being refreshed continually in a loop, very simple, clear the screen read the RSSI, then repeat.
The first set of results are with the e-paper unit ~20cms away from the ESP8266, there is a distinct 6dBm advantage to having the antenna pointing directly at the Router to having the ESP8266 being flat face towards the router if that makes sense. This result is to be expected. The reduction in power is 75% when not orientated towards the Router. Each -3dB is a loss of 1/2 power at the receiver input. So -6db is 1/2 * 1/2 = 1/4 (1-1/4)=0.75
With the display (the end where I believe the display driver chip is located - the thick white section) now placed in close proximity to the ESP8266, the signal drops from the freer space reading of -60 to -64dBm and -66dBm to -69dBm with antenna pointing at and at 90° respectively.
So all this means there is some correlation with received signal strength and display proximity, it degrades Wi-Fi reception.
If your customers experience reception problems you should advise them to point the longest edge of the PCB towards their Router, this will ensure they are getting maximum signal strength.
You could add an RSSI display to the Setup screen to give an indication of signal strength at the instant it is drawn. Anything less than -70dBm e.g. -75dBm is beyond a usable limit. I'm already at the limit of my Router range in these results and I have a nearby extender that I normally use. See my G6EJD YouTube Tech Note 053 for a chart of usable Wi-Fi signal strengths.
Also you might ask your customers to try a simple Wi-Fi signal checker and if they report Wi-Fi signals below - 60dBm e.g. -65dBm then they have reception problems, this is a common problem.
Hope this helps.
Antenna pointing directly at Router (antenna square-wave like element longitudinally pointing at Router)
E-Paper screen 20-cms away from ESP8266
SKYAE43F Signal: -60
SKYAE43F Signal: -61
SKYAE43F Signal: -60
SKYAE43F Signal: -61
Antenna at 90° to Router
E-Paper screen 20-cms away from ESP8266
SKYAE43F Signal: -66
SKYAE43F Signal: -67
SKYAE43F Signal: -67
SKYAE43F Signal: -66
Antenna pointing directly at Router (antenna square-wave like element longitudinally pointing at Router)
E-Paper screen 1-cms away from ESP8266
SKYAE43F Signal: -64
SKYAE43F Signal: -64
SKYAE43F Signal: -65
SKYAE43F Signal: -64
Antenna at 90° to Router
E-Paper screen 1-cms away from ESP8266
SKYAE43F Signal: -69
SKYAE43F Signal: -69
SKYAE43F Signal: -69
SKYAE43F Signal: -69