The cluster in the lower left represents an underdelivered audience, generating an average ROI of $0.25 for every $1 spent.
The majority of the activity is in the middle of the chart, generating an average ROI of $1, but ROI did trend higher as the percentage of ads served to a target audience increased.
The cluster in the upper right represents the impact of delivering more ads to the targeted audience, which led to an increased ROI of $2.60 per $1 spent.