If your lower down then your electricity supply is lower...i think its for every 10metres down hill you are, you lose a kw...
Also the water may get tired if it has to travel uphill extensively so that might be an issue...
Just joking bud, If your sub pump is trying to push the water to an elevation around 15/20 ft higher than your pump is set you might get a slight problem but it's doubtful...
Don, you are on the right track.
All pumps will have a 'head'. The Clarke CSE400A has a head of 8 meters. At that height above the water level the submersible wouldn't pump any water at all but at 0 (zero) head it will pump 115 liters a minute (theoretically.) As the head or height the pump has to pump increases, so the delivery volume will decrease.
The specs graph on that submersible shows that at a 2 meter head the pump will deliver 100 LPM; at 4 meters it will deliver 80 LPM and at 6 meters it will deliver 50 LPM.
I have also noticed that our water in the tank is much colder than it was 2 months ago. As the water's temperature drops its viscosity changes and this will also impact on delivery volume.
So I would suggest that a 20% drop of delivery flow at a 2 meter head (+- 6') would be noticeable.