When I fully charge two 18650 TF flames and put them in tr-j12 the torch is less bright. As cels discharge brightnes returns. I asked all my family members and they agree. I even took pictures and it is defenetly. I think that bateries are to blame…
maybe it’s because of the heat? I mean, maybe it’s brighter when it heats up? 
Do you have other cells?
Nope you’re not blind… others have reported brighter hotter performance, and greater wattage power consumption at lower Vbatt. A couple BLFers prefer to use lower voltage C-NiMH cells to boost Lumen output. I prefer the opposite scenario, 3x26650 higher Vbatt when used as a constant-ON trail floodlight. One of the hidden strengths of the J12 is the ability to fine tune performance with various battery configurations.
An old trick I have used more than once on a cold winters morning when the engine won’t crank, is after failing to start, wait a minute or so and let the heat generated internally in the battery to permeate through the acid.( in other words, the battery warms up). Warm batteries are more chemically active and will generate more cranking amps.