Each time someone claims a small LENR/CF effect, observers ask: why not simply chain many of the small effects together to make a larger effect with a similar COP? This is similar to chaining batteries together to increase voltage or current. The reason is because, in my opinion the claimed over-unity is due to a small measurement error which will not scale up as more devices are added. For example, assume someone measures that they put 50J of energy into a device and claim they measure 99J out by a more difficult, indirect manner. However, the actual output was 49J with measurement error of 50J. Now, they attempt to scale it up, as the observers ask. They put 500J into 10 reactors or a reaction mass that is 10 times larger. Instead of seeing 990J as expected, they see 540J. In other words, they are seeing the same COP<1 + measurement error they saw before but with a false COP of ~ 1.1 instead of ~2.
This might be one of the reasons why, after all these decades, the output of claimed LENR/CF successes never increases above certain levels: As they attempt to scale it up, the relatively fixed measurement error which caused the effect does not scale linearly with the output causing the COP to decrease towards 1 and eventually below 1.