I roast a Brazil natural but get high bitterness
Just what I would do, not necessarily what will bring results. It seems you’re struggling at bringing the energy from the beginning to the end, and the roast seems a bit on the long side. I would up the preheat to 305 and start with F3. Of course, we’re talking about a calibrated fan. I would also go for a lesser delta temp, which will be possible if you start with higher PH. It is not the same if you have 12.5°C / 22% or 7.5°C / 22%. Although it won’t help, I’ll just link my first roast of a Brazilian natural that turned out incredibly good. You can’t really use any of it, not just because it’s 500g, but you can have an outline of a concept.