To the OP: When I inquired about this with DRV a year ago the only option was to upgrade to an 8AWG wire which was pretty cheap to do and I would certainly recommend considering.
Now, that being said, Mark are you are saying my solar install isn't serious? I think most would agree that 1340w of LG panels, 600AH of Battleborn batteries and 2 Victron 3000w inverters isn't playing around... I too know how to use a voltage drop calculator and conscientiously did so when laying out my system. With my four panels running 2S2P I will be pushing out no more than 21 amps at a max of 82VDC. Assuming 75 volts (the lowest I have seen from these panels), 21 amps and a 10AWG wire running 20 feet, my loss will be at 1.12% which is well within the general rule of thumb of 2-3% loss for a PV system. The 10% rule is applied more to load circuits within the coach (eg. Batteries to inverter or lighting), not for the PV array to the solar controller.
So to your point, I agree that IF the OP is planning on running 24 volts that the #10 wire MAY not be the best choice. But then my first question would be why would you want to do that? Regardless, I guess I should have qualified my answer on the wire more clearly to say something along the lines of "depending on the voltage output of your panels and how you configure them (series/parallel/combination of the two) you will want to take a look at the voltage drop to determine the best wire gauge."
So let's look at this case... Four Renogy 12V 100W panels (RNG-100D-SS) all in parallel (pros and cons here I won't even get into). Vmp of 17.9 volts and Imp of 5.72, so in a perfect world we end up with 17.9VDC at 22.88 amps. Now if we are running that 17.9VDC at 22.88 amps through a #10 wire over 20 feet, that equates to a 5% voltage drop which is a bit much for my liking as well. But if we just change the configuration of those same panels to a 2S2P setup we now have 35.8VDC at 11.44 amps and using the same #10 wire only equates to a 1.28% drop which is more than acceptable and I didn't have to spend a dime on heavier wire and wrestle with a #2 copper python to get to an acceptable voltage drop.
So in summary, my humble opinion is that unless shading of your panels is a major concern, run some or all in series to up the voltage, reduce the losses and avoid having to spend a bunch of money on the larger wire and the hassle of working with it.
***TECH TIP*** Running solar panels in series requires an MPPT solar controller to handle the higher voltages.