When using data, and comparing the results of the measurements in AudienceReport it is important to distinguish between the impression profile of the campaign and the number of impressions in target group.
Campaign impression profile
The campaign impression profile will be a metric for the profiles reached with the campaign, based on number of unique profiles. This is, that even though a user is exposed for the campaign twice, the profile will only be counted once.
Impressions in target group
Impressions in target group is a measure of impressions executed in the target group. In this case, the frequency is not considered. This means that an impression will be registered as in target group, even though the impression might be the second or third exposure of a user.
Based on the two definitions above it is clear that, even though you have a lot of impressions in target group, the campaign impression profile might not be spot on. I.e. you have a campaign targeted women with 1.000.000 impressions. 75% of the impressions are exposed in target group. However, the frequency within the target group is 2 why only 375.000 impression are unique exposures. This means that the impression profile of the campaign will be 60% women and 40% men. This is, the share of unique exposures divided by to total number of unique impressions.