IIRC , a higher voltage generally means a higher efficiency due to the constant current draw for both type of cells.
However for that higher efficiency , you will lose 3 times the mAh .
And due to the lower capacity , you'll reach the point of maximum tolerable internal resistance faster which means a lower late efficiency as compared to the 18650 cells.
I could be wrong tho.
IIRC . LarryDFW has proved that empirically on another post
Yeah I think you may be talking about the current draw influencing in a li-ion capacity. When discharged at a lower rate (lower current), the battery lasts longer.
With the DC/DC converters we use, assuming we would need uh, 20W from a li-ion, that would make sense.
So we know that if you drain 5A from a crap 18650 it won't last long. Its life and capacity is severely lowered in some cases.
Anyways multiple (2 in this case) 16340 cells are better for high drain applications IMO. BUT a single (in this case) 18650 is better for size, capacity, at lower drain.
(Heck, if you're draining 20W from batts, you should just build a 3x or 4x 18650 host)