tjasak It sounds like you're trying to use 2-Point Perspective to generate a Parallel Projection image, but these aren't quite the same thing. Parallel Projection removes the perspective element, rendering all parallel lines as actually parallel ad-infinitum.
2-Point Perspective on the other hand maintains some level of perspective, but removes one vanishing point as compared to 3-Point Perspective (the default perspective for most 3D modeling/rendering software, as it is the most accurate to how our eyes/a camera works compared to the frame around it). This means all vertical edges that are parallel are rendered as such, which can help make an eye-level view look more "natural" (despite a 3-point perspective being more "accurate"). This is because your eyes are also always registering the frame of the image, which is always parallel, and seeing slight inconsistencies between these edges and the edges in the image can look weird.
2-Point perspective breaks down however the further you rotate your view down or up. As it is distorting the view to keep vertical edges parallel, when you are looking up at a steep angle it will severely distort the image to maintain the parallel projection. Thus, if you're looking to create a rendered plan this system will quickly break down and create some strange visual results.
This is why we all also want Parallel Projection (and the related axonometric/isometric/camera angle adjustments), so that we can have both options depending on what we are trying to render!
Hope that helps.