Microsoft Invest - Use a viewability rate target for guaranteed views
Because a vCPM campaign may still incur some impression-based costs, it may be necessary to manage the average viewability rate. Because a vCPM campaign only pays media cost on viewable impressions, a typical threshold for a CPM campaign (e.g. 70%) will be too high. To manage the risk of very low viewability while still taking advantage of the viewable-only payment feature of the vCPM campaign, use a lower threshold (e.g. 30%).