My experience is that the US is large enough to support multiple 2% LaL ad sets running at a time without suffering from cannibalization, even with AEO campaigns. But there are a few things to consider:
- How old is your custom audience list? If the identifiers are out of date, a large list might not be creating as many LaL matches as you'd expect;
- How down-funnel is the event? Is the event a purchase? Can you move up-funnel from purchase and still get strong signal?
- Can you segment the LaL audiences in a meaningful way based on interests or demographics and align creative with those segments?
In general, I think getting AEO campaigns to work at scale requires a lot of experimentation with creative -> audience alignment as well as event exploration. If your 5% AEO campaigns with broad targeting aren't working, then try shift to multiple 2% LaL campaigns with earlier-funnel events, or try to find more resonance in creative / audience alignment, or both.