My informal testing is complete and the newer round bodies contain drivers significantly more efficient than the older 4-flats so this swap is something that's a reasonable idea.
Details, please . Are we talking brighter at a given runtime, longer runtime at a given brightness, or a balance of both?
it may simply because the new A2 has a more efficient LEDs
I have observed that you can often double-tap a 4-flats A2 to change it from the 1/2 on stage to the normal incandescent. Generally, when I can no longer double-tap to get the normal beam, I change my batteries.
You've never seen the 1/2 on stage (often referred to on CPF as a sickly yellow beam) on an A2? Strange...