Consider researching your industry standard.
Sometimes I see my campaigns have INSANE success initially. But, as time and impressions go on, you start to see more-or-less average results.
I don’t necessarily have a solution to your question but I can tell you one thing. After time, money, & results are spent, optimize like f$%#ing mad.
Time and Data are your best friend. At least, for me it has been.
Obviously, we all want to have the highest CTR and the lowest CPA but you need something to measure against.
For example, one of my clients offers financing/loans to small businesses.
The keywords associated with that industry range from $20 CPC to $60 CPC. To make things worse, the client has only $500.
So, in understanding the competition and the industry standard that I’m up against, chose an unorthodox approach and went to social.
With that, we’ve been able to get qualified leads for less than $50.
If you were a real estate agent, you’d lose your mind(or your job) at that $CPL.
But, because I’m basing my success on industry standards, understanding the competition I’m up against, and the expected ROI from the clients KPI, I can effectively measure my success.
Might be TMI but I hope this helps