There is no way to create a uniform KSC report due to the fact that the --height and --width options specify the canvas size and not the size of the full graph. The following options are supported by RRDTool's rrdgraph command:
[-w|--width pixels] [-h|--height pixels] [-j|--only-graph] [-D|--full-size-mode]
By default, the width and height of the canvas (the part with the actual data and such). This defaults to 400 pixels by 100 pixels.
If you specify the --full-size-mode option, the width and height specify the final dimensions of the output image and the canvas is automatically resized to fit.
If you specify the --only-graph option and set the height < 32 pixels you will get a tiny graph image (thumbnail) to use as an icon for use in an overview, for example. All labeling will be stripped off the graph.