ScreenPixelsHeight & ScreenPixelsWidth should be used when IsMobile = True, as this indicates the device making the request is either a smartphone or tablet. We have these values populated against the devices in our database and the property value will return an integer value.
Desktop User-Agents are different to those from smartphones or tablets as they do not contain a model identifier (only OS & Browser) in the User-Agent to distinguish between desktop computer models or whether it is an emulator. Here is a standard desktop request from my PC - Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/79.0.3945.130 Safari/537.36
If you have any other queries you can contact firstname.lastname@example.org directly.