OK, this is pretty far out and would need someone with time and money to test this.
1. There is a small time differential between an area of low elevation and an area of high elevation. (There were experiments done on this and it has been proven.)
2. I'm suggesting that if using an Earth Battery, the energy may flow downhill like a stream (due to the time differential). So imagine the south-end placed on top of the mountain and the north end at the base; the Earth Battery may produce loads of electricity many times stronger than on a flat plain.
3. It may also work better to have several south-end electrodes funneling into one north-end electrode.