My view about LENR experiments is more or less identical to Abd (and therefore not popular here). Focussing on getting high COP is not counterproductive. Instead, focusing on understanding and reducing experimental artifacts will give better results whether LENR in these systems is real or no.
I'm writing this thread because I've just thought of an artifact I had never before considered that would affect some, though not all, of these systems in unpredictable ways.
Where the difference between control and active runs is that powder (or different powder) is put inside the reactor, and the reactor is Al2O2, we have an issue because the effective emissivity of the fuel can alter the total reactor emissivity. Further, this effective emmisivity may change largely with tempoerature, in ways both reversible and non-reversible. The range of possible effects is wide open.
It is impossible to control for this effect because any chemical difference in fuel composition could alter things.
It can be removed completely as a possible artifact by encasing the al2o3 reactor body in a known light absorbent covering.
You get this weird artifact for systems that use temperature as a proxy for heat emitted. This is inherently unsafe, because anything that alters thermal resistance to ambient will change temperature but not heat. So although this particular artifact is specific to the translucency of alumina and can be easily prevented, in general it is not easy to be sure.