<b>Running 4+ ad sets at the same audience adds a ~9% CPM tax from self-competition</b>

<b>Running 4+ ad sets at the same audience adds a ~9% CPM tax from self-competition</b>

CPM = cost per 1,000 impressions.

Auction-overlap diagnostics, 33 accounts:
— 2 overlapping ad sets: +3% CPM ▲
— 4 overlapping: +9% CPM ▲
— 6+: +16% CPM ▲ and delivery starves the weaker sets
— Consolidating to 1-2 broad ad sets recovered most of it within 5 days

You are not 'testing audiences,' you are bidding against yourself in the same auction. Meta charges both sides.

Read: every duplicate ad set on overlapping audiences is a CPM surcharge you pay to yourself.