I dun think positioning play a big role. The fan works on ###### in air from its environment. For example, if the air around your hse is warm, most likely the fan will be blowing warm air too. So, room temperature play a very impt role.
Sump above main tank??? usually setup! one of the way, which i think is expensive is to DIY a overflow box to a hangon refugium. Maybe other members got better ideas?
Overflow system comes into the picture to tackle the oil and wanted substances flaoting on the surface. The system help to flush it down to the sump . As for the water evaporation, It's best advise to drip at the sump. just my thoght.