Terrain scale differs from object scale?

I have created a terrain and left it to its default size of 2000 by 2000 units... i then added a plain for prototyping a layout for a game. resizing the plain using the scale to 100 by 100, i would expect it to be fairly small on my terrain. but no it appears to be a quarter of the size of my terrain. do objects a terrains run off of different scales? this doesn't seem correct to me.

I should clarify that my plain is laying on top of my terrain and that its not an optical illusion caused by the perspective of the scene view :)