It does not really matter.
What you want is that 5th wheel to be in a sweet spot of balance with harmony regarding weight. That tractor has a spot where the front of the 53 foot reefer or van is about in line vertically with the front of the first axle drive tires (24.5 talls which will put them about a inch or two ahead of the low pro 20’s) right about there is really good.
The only way any improvement in fuel mileage will come with the what I call a generation 4 evolution of areodymaics when additional vanes and dams are installed on both the tractor protecting and covering that catwalk space and the trailer reaching ahead of itself at the top like a airplane wing to keep the airflow from getting down in between. And even then it’s only about a .7 mile to gallon imrpovement large fleets will see big money in that, but one or two trucks fleets wont see that much. A few dollars worth maybe.
If the 5th wheel is too far forward or too far back then the tires have to fight more to make the traction happen or have too much traction taken away and so start to skate across or under or over steer way too much. And it will show up in abnormal wear soon enough. Generally 12500 on the steer 34K and 34K for 5 axles standard CMV design is perfect for the tires and they don’t mind a shift now and then a little this way or that. But not constant. Like everything else.