As I have said before and is obvious to most researchers electrolysis limits you to temperatures less than 100.. and controlling the temperature and reaction is difficult..
I don't think Staker did much after the "runaway"
How do you prevent "runaway" happening..run the expt at a max of 60C?
I understand that excuse. But Staker controlled the runaway - and ran his experiment fine at 67C.
I just have never seen as convincing gas-phase experimental results, as I have electrolysis results.
And as for larger excess heat - at high temperatures the thermal resistances that determine the temperatures from which powers are deduced are less easy to control. The input power (to get those high temperatures) is higher. For flow calorimeters better insulation is needed for high efficiency. Basically, you are just making errors in calorimetry more likely.
No-one has come up with a good reason why nuclear reactions should suddenly start at above 290C and get larger in amplitude as temperature increases.