The distribution graph gives you a better insight into the position of the traffic source in a customer journey. The distribution graph displays the total amount of touchpoints of all customer journeys from one specific traffic source in one graph. The graph displays ten "buckets", each representing 10% of the touchpoints.
When, for example, the average position of Traffic Source X is 0.5, you might think it’s always in the middle of the customer journey. But in reality Traffic Source X could also be active in the beginning and at the end of the customer journey, resulting in an average position of 0.5.