Re: DC wire run length in parallel?
What are the array specs? Twenty feet isn't very far; you should not be experiencing huge Voltage drop on that distance unless the array Voltage is low (12 V nominal) and the current is high (more than 16 Amps).
Using those minimal numbers, 10 AWG would be about 5% drop, 8 AWG about 3%, 6 AWG about 2%.
If you double the 10 AWG it's like halving the current, so each run would take 8 Amps and have about 2.5% Voltage drop (nearly the same as a single run of 6 AWG).
Four 175 Watt panels, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.
Ohm's Law: Amps = Volts / Ohms
Power Formula: Watts = Volts * Amps