First, if you go back to my earlier post, you'll see the statement that the relative humidity has nothing to do with it. Location - no. Elevation - nope. Temperature, huh-uh. Machine design and construction - yup.
What's happening here is that the back of the paper takes longer to absorb airborne moisture than the front, which is a thin layer. Both sides expand and contract at about the same rate as the air slowly changes humidity - most of the time. But, when moisture (ink) hits the front, it stretches a little, while the back (which is still dry) doesn't stretch very much at all and the paper buckles inside the paper path. After the paper has dried, the opposite can occur with a sudden change in humidity. This happened to a tiny, 2"x4" Harman FB Al print I made. It was lying flat when a big rainstorm hit, and the air became very humid very quickly. The paper curled into a cylinder the long way all by itself, just sitting there. This time, the back absorbed more moisture because of its thickness and greater absorbency while the thin front coating could only absorb very little, and the print bent toward the front into a complete circle. In this case, it wasn't the relative humidity, but the sudden change in humidity that caused the buckling. Eventually, the little print flattened back down, again, all by itself.
Second, I don't believe that the scratches are coming from star wheels. At first, with this GPH (for definition see previous post), I had star wheel marks in several of these new fiber-based and other glossy papers. By running some large, fairly thick printing paper upside-down through the machine several times, the sharp edges of the star wheels (they kind of make what looks like tiny centipede tracks) polished out and the problem went away. The star wheels still do their transporting job, and leave no marks at all. None of the marks I had gotten that I described in my earlier post looked at all like star wheel tracks. They were typically pairs of perfectly straight lines about 1/8 inch apart, with each pair at the high points in the paper's "M" shape after the ink had been deposited, and always in the direction of travel. They could be gouged out by the edges of some kind of plastic wheels, but they look more like they are made by stationary ridges in the paper path. Once or twice, the buckling was severe enough to cause a head strike in the perpendicular direction, but this was rare. Finally, by spraying the back of the paper with water and letting it settle back down, almost, but not quite flat, the problem was solved. Now, the extra moisture remaining in the back of the paper from the light spraying counters the tendency of the front coating layer to stretch dramatically more than the back, and you get a flatter paper coming out of the inking area inside the machine than otherwise.
I also use "Wide and 5" for my gap settings, but I always did after reading the wonderful web site by Eric (Mad Man) Chan when I got the machine. As mentioned in my earlier post, I also use the sheet feeder, not the back and not the front feeder, but I make sure it goes in smoothly by keeping the leading edge straight and to the back before hitting the advance button. I don't just let the GPH grab it from wherever and however the paper wants to sit in the feeder.
Since adopting this practice of spraying the backs of large sized paper (regardless of the humidity) there have been no scratches. None. I recently completed printing black and whites for a gallery show with all 17"x25" Harman FB paper and I had no wasted paper at all from scratches.
I told Harman's tech rep about my procedure. He said he was sorry I had to go through all that, but I told him it wasn't his paper's fault, and so far, I love their paper. I had previously advised him of the flimsiness of the Harman boxes, and that I dispaired of getting boxes of the large sheet size that didn't have a bent corner or two, or three, or four. He responded that Harman has beefed up their boxes and that the new packaging should be out in the market place now. Another issue was also improved by Harman; that of cost. They have had excellent sales (or so they say on their web site), and resulting economies of production, so they've lowered the prices for the Harman FB papers. The lower pricing is starting to show up in the market place. All good news.