It would be, per person is a horrible way to do it.Could be disproportionate against single person households though.
If we assume 1.0 as base value applied to one room properties.
Then add a .1 multiplier for every extra bedroom.
Add a further .5 if children or elderly.
Add full exemption to expensive units if medical exemption.
I could imagine someone like our government doing it per person though, wouldnt be the first time singletons get stood on and then packed student houses mining rigs running 24/7 on cheap units.
Also bear in mind more adults usually (I know not always) also means more income.
My sister with 4 in her house uses less than me.
House size is ok, as long as they dont go overboard, they might do something silly like assuming a house needs 3x the energy of a flat and then not considering the likely increased household income as well, the multiplier needs to be very small. I think the most simple way to go is just a X amount of units cheaper, an exemption group, and some COL provided to people means tested with children, disabled, etc.
Maybe this is why we have no use more pay more tariffs here as I guess people in big houses would think they unfair.