ONE reason to keep the ball as close to the center of the axel, is the amount of weight taken off the FA. I personally have found that the closer I can get things, the better the tow rig handles. An inch one does not notice, as much as say an addition 8-12". Hence why a lot of folks do not like to tow or haul things with vans Like the 15 passenger ext back end Ford vans. Be it the old E series, or new transit series.
I have a 350 transit I drive at work. I do not like it when I put three pallets pallets that wiegh 1500-2000 lbs per in the van, That back end pallet is totally behind the rear axel. You can feel the front being on the light side. Expecially compared to the MB Sprinters we've had the last few years. Put three 2000 lbs pallets in it, other than the total weight, handles generally speaking, as if it was empty. No real difference in steering feel etc. Then again, that back pallet is centered on the RA......
Hence why a few posts back on page 1, I mentioned preferring to EXTEND the hitch forward on the trailer to get the room one needs. Altho it is the more/most expensive option. I've done this to two different trailers. They pulled a lot nicer too! ALtho this does add a few lbs of tongue wt to them........
There is not a perfect answer frankly!
marty