Placement drift: the leak hiding in your average

The most dangerous number in your account is the one that looks fine. A blended ROAS of 3.8× doesn't prompt an investigation — it prompts a nod and a move on to the next tab. An average is a summary, and summaries are where problems go to hide.

How placements drift

Advantage+ placements let Meta's delivery system move your budget across Feed, Stories, Reels, Audience Network, and the rest, chasing whatever the optimization signal says is cheapest. Usually that's what you want — it's the whole point of letting the system optimize.

The catch is what "cheapest" is measuring. If the system is optimizing toward a signal that fires more easily in one surface than another, it will happily pour budget into placements that generate the signal but not the outcome. Cheap impressions, cheap clicks, and revenue that never shows up. The drift is gradual, it's automatic, and nothing in the interface announces it.

The average didn't lie to you. It just answered a different question than the one you were asking.

Why the arithmetic hides it

This is Simpson's paradox wearing a media-buying costume. A weighted average lets strong performers carry weak ones, and the more strong performers you have, the more weakness they can carry before the top-line number moves at all.

Run the numbers: 81% of spend at 4.4× blended with 19% at 1.1× gives you 3.8×. Perfectly healthy-looking. Cut the leak and redeploy that budget into the placements that were carrying it, and you're at 4.4× — a 16% improvement that was invisible in the metric you were watching.

Finding the leak

The mechanical part is easy: break down by placement, sort by ROAS, look at the bottom. The judgment part is knowing what you're allowed to conclude from what you see.

• Check the volume before the verdict. A placement at 1.1× on €80 of spend is noise. At €4,000 it's a decision. Small slices produce wild ratios for the same reason small samples do.
• Check attribution before you cut. Upper-funnel placements often earn view-through credit that a last-click read never shows. A weak Reels number can be a strong Reels contribution that's being attributed to the Feed ad that closed it.
• Check the trend, not the snapshot. Drift is a direction. A placement that's been sliding for three weeks is a different animal from one that had a bad Tuesday.

The reason this stays hidden

Nobody breaks down every campaign by placement every morning. It's twelve clicks per campaign, it's boring, and it's usually nothing — which is exactly why it's usually missed. The check that only matters one week in eight is the check that never gets done.

So Adgent does that decomposition on every read. It looks inside the averages for slices that diverge from the account's own baseline, filters out the ones too small to mean anything, and surfaces only the ones where the money is real. Most mornings it finds nothing and says nothing. The mornings it finds something, it leads with it.

Averages are answers to questions about groups. Your budget isn't spent by a group. It's spent slice by slice — and that's where you have to look.