This study aims at exploring ink spreading, which causes significant colour deviations in ink-jet printing. We present a method for investigating this phenomenon by considering only a limited number of cases. Using a combinatorial approach based on Polya's counting theory, we determine a small set of ink drop configurations which allows to deduce the ink spreading in all other cases. This improves the estimation of the area covered by each ink combination which is crucial in colour prediction models. Such models simplify the calibration of ink-jet printers.