Gdetrailer et al - check my math here, good catch on return path:
Simple answer, solar panel placement affects charging more than the difference between 40ft and 70ft of 10ga.
More complex answer:
Based on OP's first post the controller puts out 14v and he measured 13.8v at battery and 13.5v at battery on 40/70ft runs. This would imply with 40f he is getting 2.5A charging current (200mV drop across 80ft (round trip) at 1mOhm/ft); and at 70ft he's getting 3.6A charging (500mV across 140ft...). The reality is that his measurements etc aren't that accurate and I'm sure that he's getting roughly the same current charging with either run, the limiting factor in his charging is *not* the IR drop in the wire, but the internal IR drop inside the battery (if you will, actually more complicated). The truth is that with ~13.5v across the terminals the battery when nearly fully charged is the current limiter and isn't accepting much current.
If he did the same experiment with 50% discharged batteries (12.1v) he will be putting a larger voltage differential onto the batteries and will drive more current. In this case the wire IR resistance might come in to play but I'm guessing second order compared with sun exposure on solar panels. Assuming full 7A charging from his panels he'd be putting ~13v across the battery with 70ft (including round trip) and 13.4v with 40ft; I suspect a 50% depleted battery will draw 7A regardless of 13v or 13.4v across it, and as it charges up the battery internal resistance will be a larger current limiter than the IR drop (as evidenced by his measurements in the first place).
Thoughts?
