So that’s normal behavior if the room isn’t super cold it will throttle back and this time of year it isn’t super cold. Room temp looks at the room sensor and adjusts based upon that reading.
If you run it in stove temp that is 100% esp driven meaning if you set it on 3, that flame level is maintained based upon exhaust temp and so forth.
If room temp is giving you issues , you could have a room sensor that is reading a bit off or not in a good spot possibly getting heated from the stove and the stove is doing what it should throttling back on less heat load.
I would do a stove temp burn and I bet the flame will stay close to the same.