for example most people who are starving for ultra efficiency ask me what to recommend, and i recommend the 1212s and lots of them.
the least efficient cob in my arsenal... but at that price, stack em up and run em low current and dollar for dollar its as good as anything out there
a lot of it is thermal dissipation. you have to assume that the same dies are used across the board in all products in a given gen
so the same dies in a 1212 as an 1825, 1212 has 144, 1825 has 450
3 1212s have 432 dies (more or less the same as an 1825)
1212 is a 28mm cob = 784 sq mm of dissipation
1825 is a 38mm cob = 1444 sq mm of dissipation
(3) 1212 has 2352 mm of dissipation (63% more than a single 1825, apart from being able to be spread apart to cooler areas of the heatsink
by this reasoning, the least number of dies on a given package size should be favorable, for dissipation purposes. obviously there are design considerations about packing as many dies as possible on a chip
probably the reason crees do well at lower currents. relatively low die count on a relatively large package size.