rf is based on physics, and can be reliably modeled with prediction tools and tuned models. rf is not always predictable because the active environment (people, steel shelves, floors, cabinets, doors) are all part of the same tuned circuit, and change with time. for example, a cell phone call to a phone in a building is modified by steel in the building. reception may be improved by moving the phone near a window, or pointing the antenna in a particular direction. radio waves are affected by just about everything around us. many environmental factors influence performance. the more significant ones include steel and water, but people and electrical noise sources are also high on the list.