What i don't understand is the pace at which the area change. I see a 4 dots area, go in and start clearing then it becomes no dots suddenly even tho i didn't see anything.
As far as I understand it, it works like this - the dots on the areas are global and everyone sees the same thing, when a 4 dot area becomes available everyone who is farming warbands rushes to start opening instances of that particular area. There is probably some global fixed number of warband guys that can spawn and the quicker people kill them the quicker the zone becomes depleted.
Also I think, in order for an area to become a 4 dot one it needs to be left alone unfarmed for some time to generate a large enough number of enemies. So when people are farming 2-3 dot areas they are essentially preventing that area from becoming the desirable level 4 that can somewhat consistently spawn the named ones. For that reason merciless aqueducts and dried lake almost never have any dots and we know those ares are being farmed by tons of people constantly.
This is all pure speculation, no way to know the actual mechanics for sure unless a dev specifies.
You must construct additional pylons.