My impression is that with batch sizes that are reaching the Roaster’s design capacity, it will take max heat settings to achieve a reasonable 1st C timeframe. A 9 minute 1st C is actually OK even though you are having to use max heat to get there.
As I said, even with my 1.5lb batches, I use P9 on the power so that I’ll hit 1st C in the same time-frame you are seeing. But I also can back it off a few levels once the beans go exothermic. Unless you need to roast the max capacity of the roaster, try some 1lb roasts that will give you a better range on your settings to play with. I personally feel that the 1lb batches are sort of the sweet spot for this roaster in terms of managing power, time, ROR, etc.
ROR is an important thing to understand. As long as your cupped results are hitting the mark, I wouldn’t be too concerned about what the graph is doing. I focus on managing the roast, extending 1st C for 2-3 minutes and not running up to hard on either 1st or 2nd. Honestly, I pay little attention to the graph and more to bean development, drum temp and time. Be careful not to let the data, theory, etc overshadow plain old roasting principles that can deliver great coffee.