Actually I reckon Milo has good vision, as some caravans do have wheels placed further to the rear than central placement.
Quite often from my experiences..(which are not many) a rear kitchened van has wheels closer to rear for that weight distrubution, and it sure does make the visual of a longer length from tow hitch back to first wheels..
But then again it might be the 'jungle juice' having some confounded effect on my perspectives..lol
A key decision for the caravan manufacturer is the placement of the wheels/suspension.
I suppose that it is all about weight distribution. ie. the majority of the weight being as close as possible to being directly over the axel group but achieving around 10% of the weight on the tow ball.
My front entry van has the suspension positioned close to centre.
I have observed that most rear entry vans have the wheels much closer to the rear. I expect that this is because most of the heavier fittings like kitchen, fridge food storage lounges etc. are located towards the rear.