hello, I do agree with him regarding the cooling efficiency,and I always put the fan behind the rad on other cars, and there is a lot of room on MKIV for that... that said, it is mounted at the front on my MKIV, and cooling is fine! and 120°C is definitely too hot!
just one (silly) question: did you check that the fan is sucking the air ? it seems obvious, but it's a really common mistake ! a friend of mine blew a headgasket, just by cleaning connectors on the fan and wired it the worng way when reconnecting ...