Why does the German layout arrange timpani from high to low, left to right?

Why are the timpani in the German layout arranged with lower tones to the left? Drums which are said to have been the ancestor of the timpani were originally played in the army as a pair, one large and one small, carried on the back of a horse. It is said that the smaller drum was placed on the left side, as the rider needed to lift his right leg to mount the horse without the drum getting in the way. This practice has carried over into modern times. *There are various theories on this.