The obstacle is the allowable overall length. Either the allowance has to be broadened to allow for more length to get the optimal situation, or if you want to use that, you end up reducing the size of the trailer—going, say, to a 48-foot trailer and getting the full length that you would like to get the optimum. But then you reduce the amount of volume and load you're able to carry, because the size of the trailer is reduced.
Any of this boat tail is not a load-carrying item.