Allan, Thanks. Are you referring to 2x6 gauge hots at 3.5v each?
A 120 volt 40 amp flow all by itself will experience 3.5 volts drop each way over the wires.
A 240 volt 40 amp flow will experience 3.5 volts drop each way over the wires.
Two current flows of 120 volts and 40 amps each, on opposite sides of the line, will each experience 3.5 volts of drop one way and zero volts drop the other way. This is because (if you think of it that way) the return currents sharing the neutral cancel each other out producing zero amps and therefore zero volts dropped on that leg of the journey.
Do you get coverage you can count on? From the bag of fertilizer? From your lawn sprinklers?
OK. You are a good teacher. Another question: If the relationship between voltage and amperage is such, I need at least 10-12 amps to crank the fridge while running an additional 300-400 watts for lights. Given a 20A circuit, 120v, 220' how far above 5% vd would you go?