Marvin totally relies on the logic of getting the biggest number of conversion with the given daily budget keeping the cost at or under target CPA. In that sense, Marvin allocates budget to ad sets considering the achieved CPAs and the spend potential of those ad sets. If you are seeing a big chunk of your daily budget being allocated to a single ad set, the ad set in subject has probably shown a significantly better performance compared to other ad sets. Therefore, Marvin tries to get the most out of that ad set by allocating that amount of daily budget.

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