Perpetua allows you to set a goal on a single product or on a group of products. When a goal is set on a group of products, those products will be grouped together in the same underlying Amazon campaigns.
Perpetua recommends that customers group products into a single goal when there is likely to be significant overlap between the keywords being targeted. This is done in order to improve efficiency across the account.
When multiple campaigns bid on the same keyword, Amazon skews the distribution of impressions towards the highest bidding product. Over time, this rewards top performing ASINs and penalizes lower-performing ASINS, and can result in higher ACoS at the account level.
Though this may seem reasonable, Perpetua has been able to realize larger sales volume and lower ACoS by grouping similar products into a single campaign. This approach means that each keyword only receives one bid from the account - thus driving a more even distribution of budget across ASINs and generally what has been observed to be a lower ACoS.