As long as the fuel, whether nearly empty, half full, or totally fills a tank ... and if the vent is open to atmosphere, chemical equilibrium dictates that over time the oil will saturate with water .... and no matter how large or small the amount of air that happens to be on top of the oil .... chemical equilibrium is what drives the water uptake based on the mass of fuel, not the amount of air. The larger the mass of oil the greater the equilibrium drive to saturate it.

If the water 'drops out' as free water to the bottom and the ambient conditions (temperature) again heat the fuel it will again saturate to the maximum level .... and the oil begins to chemically function as a pump to collect water beneath it.

The only way to stop this water uptake is to have a vacuum rated tank (damn expensive) and simply close the vent valve, etc. .... the other methods already given are far simpler.
The chemically (and humidity/saturation) correct statement remains ... an empty tank will not uptake water to the degree that a partially, full tank will. If you have no oil to little oil to saturate you will have less water to provide the correct conditions for growth of the typical 'fungals' that cause the majority of fuel contamination. Then you dont need to 'dose' the tank, dont have to drain filters, and will have less vulnerability to a contaminated tank.

Your choice, as you simply cant beat mother nature (including her 'chemical equilibrium').