Why is there a difference between the level of coverage displayed in your coverage checker and my own experience?

The coverage map has been made using advanced prediction tools which we aim to make as accurate as possible.

However, the differences between predicted and actual coverage are unfortunately unavoidable due to the nature of radio based mobile networks and the unlimited variations in environment at a specific location. For example, the distance from the network base station affects coverage and geographic features like hills, buildings and trees can block mobile signals and affect mobile reception.