Not necessarily. If there's a line of sight with nothing to reflect off of, then yes, you can get maximum range. But, and keep in mind that radio propagation is not my area of expertise. I'm relying on what I remember from a college radiation physics course:

Consider a scenario where you're trying to shout across echoing terrain. The echoes and reverberations will locally amplify, or cancel out, what you're saying depending on location. If the listener moves more a few feet in any direction, then the apparent strength of your shout changes. It's called constructive and destructive interference. There's also the problem of understanding the original message among all the echoes and reverberations.

Now, apply that logic to radio waves instead of sound waves. Bouncing off various terrain features creates multiple radio signals. They constructively or destructively interfere with each other and the original signal. The original signal can get canceled out, or so buried under all the reflected signals (Low signal to noise ratio) that the receivers in the cell and/or the cell site can't understand it.

I hope that's clear enough to get the concept across.