With mCable, your TV is receiving 4K. Without mCable it was receiving HD. Now your TV may very well apply different picture adjustments to the image (this is usually called ‘Picture Size’ and there is usually a button for this on the TV remote) for HD and UHD inputs. For instance some TVs may overscan HD but do nothing to UHD, which means with HD your image appeared slightly zoomed but was missing some of the edge contents.