It's important to calculate and model on CPA Targets when you run performance campaigns. As CPA Targets are the top metric that everything depends on.

Your LTV will make your CPA change.
Your AOV will make your CPA change.

You can outbid competitors when you have a strong back end.

But it's important to have thorough and robust modelling of this CPA in order to make sure you're not killing ads too early, and also to know when certain ads have lean-way to scale.

I will upload a public jupyter notebook soon to plug in to Shopify and get your perfect CPA.