Performance Max Asset Group Dilution: The Hidden Waste Eating Your Budget

The Illusion of PMax Efficiency

Performance Max campaigns report aggregate performance. A 4x ROAS across the campaign looks great. But inside that average lies a distribution problem that most brands never see.

What Is Asset Group Dilution?

Asset group dilution occurs when Google allocates budget across multiple asset groups in a PMax campaign, but the allocation does not reflect commercial priority. Specifically:

• Display and YouTube placements consume 40-60% of budget while driving <10% of conversions
• Shopping placements (the primary conversion driver) are starved of budget
• Search placements cannibalise your existing Search campaigns

The aggregate ROAS masks this because the shopping placements are so efficient they compensate for the waste elsewhere.

How to Detect Dilution

Google does not make this easy. PMax intentionally obscures placement-level reporting. But you can detect dilution through:

1. Placement reports — check the proportion of spend going to parked domains and low-quality GDN placements
2. Search terms reports — identify branded queries that PMax is capturing instead of your Search campaigns
3. Asset group comparison — compare conversion rates across groups to identify underperformers
4. Impression share monitoring — if your Shopping impression share drops when PMax budget increases, dilution is occurring

The Commercial Impact

In a recent audit of a £30k/month PMax account:

• £8,200/month was going to Display placements with 0.02% conversion rate
• £3,100/month was capturing branded searches that the existing brand Search campaign would have won at lower CPC
• Only £18,700 was actually driving incremental Shopping and Search conversions

The reported ROAS was 3.8x. The actual incremental ROAS was 2.1x. The difference: £11,300/month in hidden waste.

How to Fix Asset Group Dilution

1. Run a placement exclusion audit — remove parked domains, MFA sites, and irrelevant placements
2. Separate brand from non-brand — use brand exclusion lists in PMax to prevent cannibalisation
3. Create intent-specific asset groups — segment by product category with relevant creative
4. Monitor URL-level performance — PMax reports which landing pages receive traffic
5. Consider splitting into Standard Shopping + Search — for accounts where PMax opacity is unacceptable

The Structural Problem

PMax is designed to maximise Google's revenue across all its surfaces. Your objective is to maximise profit from the surfaces that convert. These objectives are not aligned.

PMax does not waste your money on purpose. It wastes your money because its definition of success is different from yours.

Asset group dilution is not a bug. It is the natural consequence of an algorithm that optimises for reach when you need it to optimise for profit.