All bidding optimisation options that involve concentrated on common values are probably unhealthy and and targeting the wrong goal. Target CPA and ROAS campaigns have a very basic and intrinsic fault that for some reason many sellers don’t take note. It is the rule of non linearity of returns, or diminishing returns. If you are concentrated on a definite CPA that is below your Gross profit margin and at the tip of the campaign you reach that target and be happy about yourself you should reassess about your real goals. Is it really attaining that CPA target?Or is it maximising profit?The problem with expanding bids in CPA campaigns is that every additional conversion costs you more and the ones at the pinnacle edge can be in reality dearer than your profit margin.
So you’re creating a loss on those previous couple of additional customers if you happen to augment the bids. But on common you might be doing well and making a profit. But you may have made more profit with out those additional conversions that cost you greater than your margin.