After following multiple threads on Condensation in over covers and under pads I did a little poking.
I think folks are forgetting about dew. As long as the night time temperature drops below the dew point condensation will form from the air. That happens most nights in most places. If you want to read more:
When we sleep in a tent it somewhat restricts air flow so there is not much of a problem unless they use a lot of mesh. OTOH the temperature rise from lost heat may keep the inside above the dew point.
If we are under a tarp or under the stars it dew or frost will form on everything. Exhaled moisture and perspiration add to the load but they are not the only source. They are also possibly far from the biggest source. In short, all surfaces get wet. The only way to avoid it is to keep them warmer than the dew point.
All this collected moisture continues to follow physics. It will collect at the low points like the bottom of an over cover or hammock body under a CCF pad that protects it from getting wicked up by whatever is on top of it. Gravity is the collecting force and the impervious waterproof barrier keeps it from dripping out or being absorbed by other mass in contact with it.
If we are dealing with setups like a Hennessy under cover with a space blanket on top we see the dew from the trapped air plus any exchanged air collected on the inside of the bottom cover. If we are dealing with a bottom quilt the same moisture is more distributed and trapped on the filler material as it acts as a sponge. That is why the insulation gradually loses loft and effectiveness unless it is given an adequate chance to dry.
If you add an over cover like the Hennessy or the various pod covers it reduces the air exchanges so that respiration and perspiration become more significant. It also provides surfaces for the dew/frost to collect on.