I found before I put my first tank in that we would get up to 60 L a night as condensation from the iron roof.
When I put the tank in, this would run down into the first flush system, but because it didn't accumulate fast enough, it would always drain away before it reached a sufficient level to flow over into the tank.
So, what I did around nine years ago was to connect a hose to the first flush outflow and take the drainage to the pool.
This meant that the pool would always receive at least 10 or 15 L a night and on very "dewy" nights, it could receive up to 60 L. And of course over recent months, when we have had light rain but not enough to fully fill the tank, the drainage from the first flush has kept our pool very nicely topped up.
In fact, I have not had to add town water to our swimming pool since I put this in place nine years ago, and only once in that time has the water level come close to the bottom of the skimmer box. (And then I topped it up from the tank anyway).
It may not work for everyone, but if anyone wanted to check their own position out, they only need to drain the first flush into a bucket for a few nights to get a feel for what they are likely to collect.
PS. On windy nights, the outflow is very poor as you'd expect. We just don't get dew sometimes.