I’ve suspected that the Bullet’s fan has a cooling effect on the roast. An interesting test may have confirmed this. Starting with a hot empty roaster running in a nearly steady condition with constant power P1, I increased the fan and watched the effect on temperature. Here’s what happened:
Notice that as the fan is increased starting at 4:00 from F2 to F3 to F4, etc. the BT decreases more and more rapidly. Going back to F1 at 9:00 resulted in a positive RoR, but then longer 2 minute intervals of F2, F3, etc. again resulted in decreasing BT. So it looks like F1 may produce some heating, but F2 and above produce cooling.
This is unlike some other small gas roasters whose fan increases can have a pronounced heating effect. Good to know when comparing profiles and machine settings with other roasters.