I remember once I took my car into a garage (think it was Renault's Evans Halshaw in Aberdeen near Altens) and asked, when they were carrying out other work, if they could check to see what the deal was with my reverse, as I'd mentioned to them I was getting some crunching going into reverse. His answer was to just take it slow basically. My advice is this. Make sure the car is stopped, pause for a bit. Shift it horizontally right across, AND PAUSE, before SLOWLY sliding it into reverse. Sometimes I've no problem, other times I've to go slow. I doubt I've got a problem with this "synchro-mesh" thing as it's very rare. I'm currently working as a driver/valeter for Europcar (driving some nice cars too!) and have noticed with a lot of VAG cars (which have a push down reverse) or cars that have direct reverse, there is no problem with crunching, except if you're still moving forward trying to find that gear.
Sorry for my long winded response. Hope that sheds some light on it from my experience.
Smye