Understanding Question of Consumption Indicators

With the consumption indicator of the BC I have my problems. Up to now the BC have worked each of my vehicles differently. In the stand with running engine and inserted driving stage the BC shows no momentary consumption, what is chatty, the engine is running yes. If I let go of the brake, the BC shows a consumption of approx. 23 liters from about 10 KM/H. If, however, I drive on the country road or highway, then take the foot off the gas and let the push-off work, the consumption goes no I don’t know why. I can’t understand. I don’t work the push-off, or the BC from Volvo actually works differently than others. Background to the demand, the pock sucks like a hole. Even on the highway at a moderate speed I don’t get below 11.5 liters. I don’t like to think about what the poop will blow away when I have the trailer on it. Greetings