Why do impressions not match between AA and Microsoft Advertising?

We've recently implemented advertising analytics. Our AMO impressions, clicks and spend data matches the google ads platform. However, for Microsoft ads our impression figures are 16% lower in AA than Microsoft ads. Our Clicks and spend data is 1.8% lower.

On a campaign basis we've identified that the variance is mainly from dynamic search ads. Are there any set up variances required to correctly capture DSA data in AA?

Thanks