In this connection, about 20% of matter and energy is transferred from first-order consumers to second-order consumers?

The food of herbivorous heterotrophs (primary consumers), to which we include representatives of parasitic plants and herbivores, are biomass producers (in other words, organisms producing the total mass of plant, in this case, bionts). And the food of predators, as well as parasites of primary consumers (secondary consumers), will be the herbivores themselves. The assimilation of food by primary consumers will be less effective (fiber is difficult to digest, and it is the main component of plants).