Format yes, but also with color. The color palette of the sunday comics was punchy and vibrant to attract attention. He very much desired to work in pastels and earth tones and it was a battle for him to get the look he wanted.
Ah, yes, IIRC, most comics are drawn with simple outlines and then numbers are written over the blank spaces to indicate what colors they should be, a la paint-by-numbers. Whereas Watterson wanted license to color things himself using whatever media.
