All Terrain Tire tread wear expectations?

Hi All. I had a set of Cooper Discoverer AT3 4S fitted and balanced last week, wheel alignment was also done. Front tires look good, but I am noticing a darker edge on both the inside and outside shoulders on the rear tires, indicating that they seem to be seeing more friction there than the rest of the tread profile. Photos attached. I checked pressures, all 4 are roughly the same, one rear tire had a little less in it, and that one has marginally more wear indications than the other rear tire. Still they're all roughly around 36 PSI. I might have understood this kind of wear on the front tires, given that steering forces might create this, but it's the rear wheels showing this. Should I up the pressure in the rear? Most driving has been asphalt so far, but on some FSR exploring on the weekend, the ride was fairly bumpy so I'm not super keen on inflating much higher. With that said, I want to maximise tire life, this was an expensive investment and I don't want to piss it away because I'm not paying attention. Any ideas? It's probably obvious, but this is the first set of AT tires I have ever had on a vehicle and don't know what to expect.