I use weight behind axle when running plow to offset weight of plow hanging off front. But for a van or any rear wheel drive vehicle you want the weight directly over rear wheels to push them into ground to provide as much psi as possible to tires. The weight behind the tires would have the effect off lightening front end not putting enough psi to those tires for stearing.
That is entirely dependent on the particular vehicle and it's current weight distribution, wheelbase, tire and axle configuration, etc. All vehicles have very different handling characteristics that any competent driver can adapt to. A maxed out trailer tounge weight on an otherwise empty standard cab 1/2 ton pickup is not necessarily a disaster waiting to happen. If it was, the ditches would be full of them. I've driven everything from a VW Baja bug to a bobtail tractor on snow and ice and many others have as well without crashing. No, neither has an ideal weight distribution. The former tends to under steer and the later tends to oversteer, but they are both drive able and the rear heavy VW is capable of getting around very, very well on snow and ice with a competent driver.