Modern OpenGL Problems with Orthographic Projection

I'm going straight to the point. I've already done some re-research and I still haven't figured it out.

I have a program that draws a cube on each face with a color. Then I rotate this cube in the Y-axis as well as the X-axis (-45 and +45 respectively).

The problem is that it hasn't been rendered as I expected, the cube gets cropped at some point.

Code:

projection = glm::ortho(-1.0f, +1.0f, -1.0f, +1.0f, +1.0f, -1.0f);

camera = glm::lookAt(
                     glm::vec3(+0.0f,+0.0f,+1.0f),
                     glm::vec3(0.0f,0.0f,0.0f),
                     glm::vec3(0.0f,1.0f,0.0f)
                     );

model = glm::mat4(1.0f);
model = glm::rotate(model, -45.0f, glm::vec3(0.0f, 1.0f, 0.0f));
model = glm::rotate(model, +45.0f, glm::vec3(1.0f, 0.0f, 0.0f));

mvp = projection * camera * model;

      

        
        
        
      

    

All vertices that I define are executed with ± 0.25. So I thought that with my zNear and zFar values, they would still fit in the volume, but when I changed the line

projection = glm::ortho(-1.0f, +1.0f, -1.0f, +1.0f, +1.0f, -1.0f);

      

        
        
        
      

    

for

projection = glm::ortho(-1.0f, +1.0f, -1.0f, +1.0f, +2.0f, -1.0f);

      

        
        
        
      

    

it works just fine

But this doesn't work with

projection = glm::ortho(-1.0f, +1.0f, -1.0f, +1.0f, +1.0f, -2.0f);

      

        
        
        
      

    

Can someone explain to me why? I mean, I know that if I add more values, the projection cube will have a larger volume to make it look just fine. I know the bottom-right vertex is outside the cube with zNear and zFar to +1.0 and -1.0 (vertices value around 1.76 after applying the matrix), but if I extend the zFar cube to -2.0f, it just has to fit just wrong is it?

I tried to read something in the Red Book, as well as the book by Peter Shirley "Computer Graphics Fundamentals". I even made the matrix myself, but with the same results.

Anyway, thanks in advance!