If an aircraft achieves its lowest "miles per gallon per seat" at take-off/climb-out, would not the carbon contribution per seat/mile of domestic aircraft be higher than that of long-haul?
No because the tax is on the total amount of carbon you put into the atmosphere not the amount of carbon per kg/km or some other ratio. So flying to LA in a 747 is going to be more polluting in carbon tax terms than flying Adelaide to Melbourne.
If you went to a carbon tax on carbon emission per kg carried this would destroy the car industry, who in turn would come down on the governments of the world like a tonne of bricks and the next you know you will wake up one day and the carbon tax issue has suddenly disappeared.
Aviation could be made more efficient by enforcing a law that means you have to fly 95% load factor. Unfortunately that would mean people would be inconvenienced and no government will be willing to enforce that type of law.
If the world was serious about climate change they would need to break the power of the petroleum/car manufacturers/chemical companies and get rid of petrol powered cars. Abolishing coal powered electricity would also help the cause. And maybe let's have a look at all the patents that have been bought up that have hindered the development of alternative/free/electrical forms of energy. Why did they have electrical vehicles in the 19th century and not now??? People need to be encouraged to have solar powered homes and they need to address the whole nuclear issue. Mass public transport in major cities needs to be the only way of getting around. (Why does the east coast of the US have great public transport but not the West Coast?)
Until that happens no one is serious about reducing carbon pollution.