I think I found a profitable campaign. Yay!
But I noticed that the conversions only come from 4 publishers (so far).
https://imgur.com/a/TWIRGVF
Is this common that only a few publishers account for all the profits?
And I'm still testing but my instinct says to create a separate campaign, include only the profitable publishers, and any other optimizations. Your thoughts?
What kind of traffic is this?
Anyway, it's pretty common that not all zones will be profitable 
Over the time as you run the campaign, more and more zones will appear and might give conversions.
Your job then will be to "kill" (block) the bad ones, and leave only the good ones.
You can do also whitelist as Matej suggest, but not all traffic sources like this approach + over time you may just saturate those zones and the performance will go down.
But anyway it's a good way to practice blacklisting/whitelisting and make some small profits 