How to find best "Target CPA"

Hi there,

im running fb ads, google ads and native ads. Im able to get positive ROI, but i had very few conversion.

Random example 1:

When i made conversion, i earn 100 $.
My ad cost ( CPA ) for make that conversion is 50$.
Profit per conversion is 50$.
In this case, i generate 1 conversion / day = profit 50$ / day


Is it great result, but i got very few conversion. What i want achieve, is generate more conversion, and i will be able to do it with increase CPA.

So in that scenarion, the second example will be :

Random example 2 :

When i made conversion, i earn 100 $.
My ad cost ( CPA ) for make that conversio is 80$.
Profit per conversion is 20$.
I generate 3 conversion / day = profit 60$ / day

( i got more conversions because increased cpc = more traffic )

So, basicaly, when i earn 100$ per 1 conversion, every ad cost ( CPA ) that is 99$ or less is profitable. But with 99$ cpa, i must do a shitload of conversion to be worth it.

And there is my question : How to propper calculate target CPA to achieve the best profit? ( optimal number of conversion + optimal ad spend )

Thanks a lot in advance

I just take the Click Through Rate (CTR) and the CPM or CPC as well as the conversion rate to work out my average cost of acquisition and then add on a margin for profit.