1-to-1 pixel mapping has nothing to do with how you set the zoom lens (optical zoom). Acheiving such 1-to-1 pixel mapping means you are feeding an input signal with the same resolution as is the native resolution of the projector (1080 x 1920 in the case of your HC4000) and also you are not applying any scaling or video processing, such as using the projector's keystone correction adjustment or digital zoom or stretch functions, which would alter the original image size or shape. Moving the projector to the shortest allowed projector-to-screen throw distance for your size screen means you will be setting the optical zoom to maxium (i.e., to produce the largest image). This setting will give you the brightest image since the zoom lens will have less light loss at this setting as compared to mid or minimum zoom. However, depending on the specific lens and projector, the image might be a little sharper or with a somewhat higher contrast by moving the projector back further from the screen and change the zoom setting accordingly. However, some projectors are capable of fully resolving all of the the pixels throughout the full zoom range of the lens (such is the case with both the Epson and JVC projectors that I currently own and I think you will find this to the case with your Mits HC4000).
Blog + Reviews + Articles: projectorreviews.com