I think it's important to note that the signal strength is related not just to the antenna's orientation and the absence of obstructions, but also to the state of the RC's battery charge.
As the battery in the controller get low, it will reduce the effective range in much the same way as turning the antenna away from the the aircraft or putting buildings, trees or hills/mountains in between.
I believe this to be the real reasoning behind the VLOS rule. It's less about actually seeing the drone than it is about preserving the maximum strength of that signal for precise control. Perhaps Line Of Sight might better be known as Line Of Signal.