Hi Desmond, my better roasts generally see BT catching up to but not crossing ET at the end of the roast. I have seen them cross on some darker roasts which I generally avoid. Also I think probe placement will have something to do with the spread.

Cheers

Ian

If BT ever exceeds ET, it means you are dropping ET faster than the beans can keep up with, such as full on exhaust with heat completely off. You would never see it in a normal roast with properly calibrated sensors.

I have some modifications on my hottop, most important was to reverse the fan and to insulate under its jacket.
I use a variac to boost voltage and I use a killawatt to view the draw, I adjust the variac to provide 122ish all the time.
I have thermocouples in the chamber for et and bt, and I use roastlogger through a mac laptop.

I am able to roast 250g, I charge at 350f based off of the bt probe.
I try to hurdle 300f bt in 5min, at 100% power, no fan. I also put a silicone trivet over the top mesh screen to block heat from escaping.
From there - its 80-90% power with a slight mix of fan and removal of the trivet, as the et approaches 450. This keeps the beans and chaff below scorch level, as evidenced in the tray.
1c is in the 9 min range, and I shoot for between 20-25% of added time and then dump. There is a general theory of less power and more fan along that 2-3 minute more path. I have many recipes saved.
If I choose to use less grams in a charge, then its just a matter of moderating power to lower the ET heat.

I also made a new cooling tray in 3 minutes of diy. I folded a good sized shipping box, putting all flaps inward so its a square tube. I droopped in one end a large section of metal door screen, with enough sag to make a flat about 1/4 depth. I trimmed and stapled the screen over the rim in 8 places. I place this on a box fan and it blows through the box/screen/beans, and its easy to pour out of a corner with the cooled result. Very fast results, super cheap.