Smith, the mini-harvesters can definitely do outer sector mining. I have approximately 11 harvesters mining on 3 different planets, 4 sectors away from my home world.

I think what they mean by "ideally situated for 6 sectors or less distance" is that the rate of return would be lower, as you would get less ore per hour if it was over 6 sectors away. That's why I have 4 harvesters on each planet 4 sectors away. That way I'm getting 1Ku CO every round trip the 4 harvesters make. And I'm slowly reducing the planet's stockpile of Ore, so I know I'm taking more per hour than it can replenish. So I'm ahead of the curve there and not easing my unit slots on gaining nothing. I'll start dialing back the number of harvesters per planet when I. Get closer and closer to 0u of CO