Hmm, think I'm out teching myself as well....
At each corner of the van, you're trying, despite all the forces - sideways, up/down, engine or braking torque, to firstly keep the tread flat on the road. Also it would be nice to keep the body level and not rolling too much. Some of these are independent, some linked.
On a 'live' rear axle, one of the main things when putting power down is the torque also tries to twist the leaf spring resulting in undesired 'lifting' and 'unwinding'. One solution was the fitting of 4 struts/links to resist the torque, or even use it to control squat. It doesn't, AFAIK, change the cornering handling much. Also, on the Connect, I don't think it would do too much as your only handling braking torque not the engine power.
Next simply, imagine looking at the two rear wheels on the end of the axle from behind with only one going over a bump. Do the treads stay level on the road surface? Now think of the FRS doing the same. Treads (and grip) stay level(ish) as they go up and down. So control of grip and going around corners with the Independent Rear Suspension (IRS) should be better......
I think thats why, despite the cost pressures and move to FWD, there was on RWD the move from leaf springs and solid axle (MK1/2 Escort), through half leafs (Capri), multi link solid axle (Mk4 Cortina) to IRS (Sierra & Scorpio).
Even on FWD there have been interesting developments at the both ends. At the rear we've seen the crude rear end of a solid (live) axle and cart springs on vans (not usually required to go fast round corners), torsion beam and coil springs on Escorts, McPherson strut and Short/Long Arm (SLA) (Saloon/Estate Mondeo). All attempting to optimise the way the rear wheels change camber and toe as loads change and they move. The last also illustrates the conflict between widest load floor (estate/van) and struts/ dampers intrusion.
So, if you want your van to go around corners, rather than just parade, you need something better than a live axle; graft in a multilink IRS rear end from a current model (FRS ?) should be the easiest.
Martin