Asset_group_asset vs Asset_group Metrics Discrepancy in API

[Dani Buchsbaum]

I'm pulling asset_group_asset metrics from the API and seeing something strange.

For a given date range, the asset-level data shows:

• Impressions: 12,469,025

• Cost: 929K (after dividing cost_micros)

For the same asset groups and dates, the asset group–level data (which matches the Google Ads UI) shows:

• Impressions: 14,460,243

• Cost: 333K

I understand that asset-level metrics aren't perfectly attributed and are often inflated, which explains why cost and other metrics are 2–3x higher at the asset level.

But it feels inconsistent (and potentially incorrect) that impressions are actually lower at the asset level.

Why would impressions be lower when all other metrics are inflated? Is this expected behavior, or a possible issue with the API?