I did come across the designs of those generators during my initial research and like you I did think the placing was the not the best though it is explained that by doing it that way you also get to use the light of the lamp. Even with the placement and lamp they're still generating 2 watts...
Like the title says I was wondering if it would be possible to generate a couple of watts of electricity from a kerosene or gas mantle. Less than 0.5% of the energy in the fuel is being converted to light which means that in the 33kJ per mL of kerosene nearly 9 watts is being lost as heat...