Unity and ARToolKit - Can the marker be placed in perpendicular to the camera?

Hello,

First of all, I have to say that I have just started learning about Unity and AR. I decided to try first with ARToolKit basically because it is open-source and I could create my first applications using markers.

The only issue I'm facing now is when I try to place the marker perpendicular to the camera. Imagine I draw a cube with one side paralell to the marker, if I place the marker perpendicular to the camera, what I expect to see is the top side of the cube, but it looks like ARToolkit (or Unity) always introduce a minimum angle to the 3D image so I can always see more than one side. If I move the camera, due to this effect, the movement is not smooth at all. Does anyone know if this is normal or if there is any way to remove this minimum angle?

Thanks!!!