In short I don't think it's going to make a huge difference, but it is going to make some difference. It's exactly like adding an aftermarket air filter to a car, swopping your flashlight's lens out for a UCL lens, redoing solder points, and all the other things we do in this hobby. If a flashlight is just a light to you/a person, then wrapping the drop-in is going to be pointless, because an XML T6 is already more than what you need, but if you/a person are a flashlight enthusiast seeking to optimize and get the most efficiency out of the LED and battery, then it makes sense to copper wrapping the drop-in.
A more thorough test would have been to measure the drop-in and LED temperature directly. But any extra heat that the copper wrapping can draw away from LED will mean more lumens, even if its only 10 more
And another point, the wrapped host only used 0.23v (4.15 - 3.92) in 20mins, whereas the unwrapped host used 0.28v (4.16 - 3.88), which means that because the wrapped host dissipates heat better, the LED can operate more efficiently. Again, it is a small difference, but it's 17.8% ((0.28 - 0.23)/0.28*100) more efficient.