I find most high density coffees do well in this roast development range and drop temp. If I go longer and hotter, let's say to 400* it loses acidity and picks up astringency. Beyond that (415*) the acidity is mostly gone, but so is the dryness. The trick is to get it hotter faster and build the pressure in the bean early. This pressure, like a pressure cooker, helps force the heat transfer to the inside the bean quicker.
If you have the time, basically what modes (no detail requested) did you do to your roaster. Your declining ROR is impressive. I have a Diedrich IR5. I have very little control, except for gas 3-22Mbar and fan 50 and 100%(I.e two setting only). Should you have any suggestions as to what I could do to have more control over my roast, I would be grateful