Differently aged impact melt in lunar samples is key to unveiling the early bombardment history of the Moon. Due to the mixing of melt products ejected from distant craters, the interpretations of the origin of lunar samples are difficult. We use numerical modelling for a better quantitative understanding of the production of impact-induced melt and in particular its distribution in ejecta blankets for lunar craters with sizes ranging from 1.5 to 50 km. We approximate the lunar stratigraphy with a porosity gradient, which represents the gradual transition from upper regolith via megaregolith to solid crustal material. For this lunar setting, we quantify melt production relative to crater volume and derive parameters describing its increasing trend with increasing transient crater size. We found about 30%-40% of the produced melt is ejected from the crater. The melt concentration in the ejecta blanket increases almost linearly with distance from the crater center, whilst the thickness of the ejecta blanked decreases following a power-law. Our study demonstrates that if the concentration of distant-derived melt of a certain age in lunar samples is rather high (>30%), it could originate from large craters (>10 km) located hundreds of kilometers away.