I could be wrong but thought the size of the LED/emitter was smaller for the XP-L. A smaller emitter within the same sized reflector should inherently throw father. But again could be wrong.
Edit. I wonder if the actual emitter (glowing part ) is smaller or just the platform which supports it. If it's just the platform then I would be wrong in terms of throw.
Your last sentence is basically right.
I managed to find a nice clear picture below of an XM-L2 that I think can be used to understand it.
The big square base is the ceramic substrate, which is often sapphire, but Cree uses silicon carbide. This acts as a physical base structure, plus as the thermal and electrical connection to the circuit board. Among other things, a wide base provides a good thermal path to get rid of heat into the circuit board (which, usually having a metal core, can then transfer that heat to the flashlight body). XM, XP, and XQ are different Cree substrate families.
On top of that is the die of the LED itself. This is the actual doped silicon that emits light. Unimportant for this discussion, but you can also see the wires that deliver power to the die, and the yellow phosphor coating that converts the blue light of the LED into a relatively full spectrum of white light. I guess L, G, and E are different Cree die families.
Lastly, there is the optical dome that helps shape the light emitted by the LED into a pattern flashlight or light fixture designers can conveniently work with. A bare die would emit light mostly upward, but the dome spreads it out more.
I'm a little unclear of the details, but I think part of what Cree managed to do with XP-L was improve the thermal conductivity of the substrate so it could be smaller for the same power level. To get a good light pattern from the same size die, however, they had to keep the same radius on the dome, which means the light is distributed in a similar manner to almost the full flashlight reflector...with the minor exception of at the edges of the LED, where they squared off a small portion of the edges of the dome to fit on the smaller substrate. This slightly alters the pattern, but not much.
In contrast, the XP-L HI, with its flat dome, does have a very different pattern. With the light not coming from a radiused dome, Cree describes the HI flat dome as "appearing smaller" to the reflector.
Also, the XP-G2, with the same size substrate as the XP-L, is able to use a smaller dome because it has a smaller die. That smaller dome likewise results in a tighter focus from the reflector, but the smaller die can't produce as much light as the XP-L.
Put this emitter in a new easywhite 18650 headlamp please.
It seems like a certainty they will. The specs they're showing are too good to not upgrade their best lights with the same. I think the AA models are getting it first simply because they were in most need of updating.