Perhaps I'm missing something here, but....
The display which goes inside your home, is there any way to adjust the full scale values?
For instance...
Boiler runs at around 21Kw when heating the tank of hot water. The gas oven hob at around 4.50Kw / 11.36p per hour. The 4.50Kw shows consumption way off the top of the 'analogue scale', the 11.36p way down the bottom of the scale, the CO2 again way off the top of the scale.
It seems to me, that all three (KwH, costH, CO2) ought to produce similar movement of the 'analogue scale'.