Hotspot Tethering meaning, your using your Phone for EE Mobile Data and then sharing this connection (Tethering) to another Device via the Phones WiFi Connection (Hotspot), I only ask as confirmation as to your set up.
If the above, then the EE Data Speed Connection is with your Phone, after this point any 3rd Party Device that is connected to your Phone is relying on the WiFi quality to your Phone and will quickly deteriorate as you move further away from the Phone. So its a 2 part connection and a fine balancing act between the two, and the best way to improve the overall connection is to get your Phone High Up near a window (try different locations around the Home) then operate the 3rd Part Device as close as possible to the Phone.
You could try doing Speed test from the Phone, then a speed Test from the Connected Device then get a feel on your WiFi Speed loss between the two Devices, you could also try switching between 2.4Ghz and 5Ghz WiFi Settings on the Phones Hotspot Settings (if you Phone Supports 5Ghz Hotspot) as 5Ghz should always provide a better WiFi Speed but a lesser WiFi Range compared to 2.4ghz.
