composition- managing distant view of large objects I'd like to simply create a mountain range,and the scene has to be fairly low angled. My test render for the scene is as shown below: 

The mountains are approx 500 meters from the camera, and they need to appear big and in composition they should acquire 50% of the scene(i.e. with the horizon which is the lake in this case). Firstly I based this off of actual distance range in real life because I couldn't come with other ways, so I put the mountains 500m from camera and made them approx. 100ft tall but then they consumed the sky. Then I had to shrink them down. But, as you can see now the problem with the scene is that, the mountains look like small hills that I fairly close by and the horizon a small puddle, whereas I'd like them to appear far from the camera and the horizon should look like a vast ocean.    

How do I achieve this? I'll attach the .blend below with the textures packed.

Here's the link
I think the main issue here is simply the viewpoint - in your scene the camera is actually about 54m above the surface of the lake; Suzanne is scales at 38m. As we (as humans) are used to viewing the world from about 1.5m above the 'floor', this throws out the perspective, giving the impression of a much smaller scene.

By simply moving the camera to about 2m from the surface of the lake you can get a much better perspective, making the mountains look much more distant :



Note that for added effect you could add a mist-pass in the compositor or blur based on distance for more realism.