You're using confusing terminology. You potentially understand the concepts correctly, but using the wrong terms will confuse people.
Multipliers refer to lobby settings. If you set metalmult to 2, it means all metal extractors now produce double the preset of the map. Any metal spot that was supposed to produce 2.4 now produces 4.8.
Without messing with lobby settings, to increase income, you need to capture more mexes and/or connect mexes to grid, then add more energy to the grid. The more energy you add the more metal you produce through overdrive, but the less return per point of energy you get. Doubling your energy does not double your overdrive. Early on, it might be advisable to form a grid connecting most mexes using solars or wind gens because you produce more energy as you connect the grid. Pylons are great at expanding your grid a reasonable distance, but they do not produce any resources.
Energy produced as part of a grid is always funnelled to whichever mex gains the most metal per point of overdrive energy. The greater the base metal production value is for a mex, the more it benefits from overdrive. As you expand your grid, you may notice that some mexes use significantly less overdrive energy and some WAY more.
