The bow Lukasz is shooting is made in Mongolia for "tourist" trade and is not what the Mongols conquered most of the world. The bow that is made in Mongolia now is more of a Manchurian style bow.
The bows the Mongols used were more like what we call a Crimean Tatar they were shorter and the siyahs were smaller at least that is one theory. The other theory is the bows resembled more of what we know call a Magyar bow with longer siyahs, longer riser area and shorter limbs. What is true is that they were shorter then the "Mongolian" bows of today.