Performance Max gives B2B SaaS advertisers two real steering wheels: search themes and audience signals. Everything else is creative and budget. Yet most accounts set both once at launch and never touch them again, then wonder why PMax drifts toward low-intent traffic. A r/PPC thread asking for a best-practice loop for iterating on exactly these two inputs is the prompt for this post.
Below is the tuning loop I run on SaaS PMax campaigns: how to read the signals, what to add, what to prune, and at what cadence — so the algorithm converges on your ICP instead of wandering.
What search themes and audience signals do
Search themes let you name up to 25 keyword-like phrases per asset group that tell PMax which Search queries to pursue. They are not keywords — there is no match type and no bid — they are directional input for the Search slice of PMax inventory. Audience signals are a separate hint: customer lists, converters, and custom segments that tell the algorithm where to begin its search for buyers.
The word that matters for both is directional. Neither is a hard restriction. As Google frames it, audience signals are “a starting point” the algorithm “expands beyond when it finds additional high-value users.” That property is a gift for prospecting and a trap for the impatient: give a weak signal and PMax expands into cheap, off-ICP traffic fast. Tuning is the work of keeping the starting point sharp enough that expansion lands on real buyers. If you are still deciding whether PMax belongs in your account at all, start with should B2B SaaS run Performance Max.
Start with the strongest signal you have
For B2B SaaS, first-party data beats Google’s interest categories every time. Rank your audience signals in this order: current customer list, high-intent converters (demo requesters, qualified trials), CRM-sourced SQL lists, then a small number of custom segments built from competitor and category search behaviour. Feed the top of that list first. Google’s in-market and affinity segments are the weakest hint you can give and should be a last resort, not a launch default.
The reason is signal density. A customer list of even a few thousand real buyers describes your ICP with far more precision than “in-market for business software.” The tighter that seed, the better the expansion. This is the same logic behind good audience targeting for B2B SaaS — the difference is that in PMax the signal guides rather than restricts, so quality matters even more.
The two-week tuning loop
Run this on a fixed cadence. The discipline is as important as the edits: PMax needs roughly two weeks to stabilise after a meaningful change, so batch, edit, then hold.
- Read the search terms and insights. Pull the search-terms and audience-insights reports. You are looking for two things: which themes are attracting on-ICP queries, and which audience segments the algorithm reports as driving conversions.
- Prune themes that pull junk. If a theme is bringing in queries from the wrong company size, wrong intent, or a competitor’s free-tier hunters, cut it. A vague theme like “software” will always broaden badly.
- Add themes from what converted. Mine your best converting Search campaigns for the phrases real buyers used and promote a few into PMax themes. Keep each asset group to 5-10 tight themes, not 25 loose ones.
- Refresh the signal. Update the customer and converter lists so the seed reflects recent won deals, and retire custom segments that the insights report shows are not contributing.
- Hold for two weeks. Make no further steering changes until the next review, so you can attribute movement to the edits you made.
Structure asset groups so signals do not bleed
Tuning only works if each asset group has a coherent job. The most common mistake is one asset group holding every product and every theme, which forces a single blended signal to serve unrelated audiences. Split asset groups by ICP or product line so each carries its own themes and its own signal. An enterprise-security asset group and an SMB-self-serve asset group should never share a search-theme list — their buyers search differently and convert at different values.
Themed asset groups also make pruning legible. When a theme misfires, you know exactly which segment it polluted and can cut it without collateral damage to the rest of the campaign. If your structure is muddled, fix that before you tune — a clean campaign structure built on intent tiers is the prerequisite for signal tuning to mean anything.
The metrics that tell you it is working
Do not judge tuning by conversion count alone — PMax can inflate that with cheap, low-intent conversions. Watch three things across review cycles. First, the intent quality of incoming search terms: are they getting closer to buyer language or drifting toward informational queries? Second, downstream lead quality — SQL rate and pipeline contribution from PMax, not just form fills. Third, cost per qualified outcome, which should trend down as the signal sharpens.
If conversions rise but SQL rate falls, your tuning is training the algorithm on the wrong outcome, and the fix is upstream in the conversion set rather than in the themes. That failure mode is common enough that we wrote a full teardown of retraining PMax off micro-conversions. For a broader health check on a campaign that has drifted, our PMax audit walkthrough covers the full diagnostic.
Why patience is the hardest part
The temptation with PMax is to treat every weak week as a reason to change something. That instinct is the fastest way to keep a campaign permanently in learning, never letting any signal mature. The operators who win with PMax make fewer, better-reasoned changes and give each one room to prove out. Two weeks of holding after a deliberate edit will teach you more than two weeks of daily fiddling.
Set a recurring calendar block for the review, do the loop, and then close the tab. If you want a practitioner to run the first few cycles with you and calibrate what “on-ICP” looks like for your segments, a focused consult can set up the reporting and the first prune in a single session.