The Bundeswehr was interested in a more offroad version of the syncro. Plus it had to be stable enough so that the doors could still be opened when a bomb exploded next to the road. VW then developed the 16 inch syncro.
One of the typical differences between the 14 inch and the 16 inch syncro is the reinforcement panels on both rear sides, the small panel on the B pilar below and the panel in the corner of the B pilar and the opening of the passenger's door.
If you like to use your syncro offroad and you want to give it some upgrades, this is definitely one of the upgrades to consider.