ICAR-DMR mixes grain spawn at 0.5 to 0.7 percent of the wet compost weight. Its Hindi farmer folder gives 0.5 to 0.75 percent, which is 500 to 750 g for 100 kg of prepared compost. More spawn is not better: it costs more and adds heat.
Mix so grains are spread through the whole mass and not left in a band. The manual fills polythene bags 12 to 15 inches deep, or shelf beds 6 to 8 inches. The folder says 10 to 12 kg per bag, because a deeper bag overheats in the middle.