Killing a 14-interest stack cut CPA 27%

Killing a 14-interest stack cut CPA 27%
DTC skincare brand, single ad account, 60d test, $140k spend.

The move: collapsed 14 interest ad sets into one broad targeting campaign (no audience definition, let the algorithm find buyers) feeding 6 creatives.

CPA (cost per acquisition, dollars to get one purchase):
— Interest stack: $42
— Broad: $31 ▼27%

CPM (cost per 1,000 impressions) rose from $19 to $24 ▲ as broad hit a wider, pricier audience — but CVR (conversion rate, purchases per click) climbed 0.9% to 1.4% and carried the result.

Read: narrow targeting was paying a premium for worse converters.