Is your PH temp set to the highest already? My PH for my 1kg batch is 572F / 300C IBTS which gives me a 407F / 208C BT temp once it stabilizes (20-25 mins preheat time for 1st batch of the session)
My FC time on a 1kg with the 572F PH is about 9 mins on average (Ethiopia Agaro seems to be a bit faster every time, just after 8 mins).
For me a BT charge temp of about 400F / 204C is about right. Eons ago when I took a 2-day roasting class on a 12kg Probat (gas fired) the instructor did say a temp of 400F is a good starting point on a roaster like that. Use that info for what it is worth.