At the risk of being shot down in flames.....
My staple roast is PNG Kimel.
My thermometer indicates First Crack around 183C degrees give or take.
So I aim for that at the 10 minute mark.
This means I aim for 65C at 1 minute with a 13 degree increment per minute.
That reaches 182 degrees right on 10 minutes.
Second Crack is generally around 203C.
I aim to reach that at 16 minutes but not less than 14.
I hope you dont think HG height ill be set and forget, because its not.
You will have to keep adjusting as you watch the roast.
Your starting point sounds fine but there are a lot of variables:
Heat gun temp
Airflow (fan to cool HG and disperse chaff)
Consistancy will come with practise.
You will learn what works for your setup and fine tune accordingly.