Radio signals, including WiFi, decrease as the square of the distance. So, double the distance, 1/4 of the signal. Triple the distance, 1/9 of the signal, etc. So, yes, as you move away the signal declines. But just moving to another room, with nothing interfering with the line of sight to the router, should not affect the signal reporting that much. However, the frequency of the WiFi is also used by other wireless devices, so the decline could be due to interference rather than just signal fading. One way to reduce the impact is to force the router and iPhone to use 5gHz instead of 2.4 gHz. To do that, you have to set up the router to have two networks, one on 2.4gHz and the other on 5gHz, with different names, then connect the iPhone to the 5gHz network. However, 5gHz signals are more attenuated by intervening objects, like walls, floors, furniture, etc, than 2.4gHz so you have to see what works for you and what doesn't.