"Proper" is good in quotes, as in "preferred." I don't think there's a right or wrong here, though behind the bars is a lot more common. I've always routed my cables in front of the bar, they stay out of the way better, handlebar/cockpit is cleaner. Functionally no difference. When I wrenched in the early '80s our shop and a lot of others routed in front of the bars.
Yep, I agree. I also wrenched in the 70's and 80's. The main issue with the front routing is that on smaller frames with stems longer than 70mm or so, the cable to the front brake can get a bit sharp. Not so much an issue on larger frames. The rear cable does not matter nearly as much.
Most C&V folks tend to stick with the rear routing to maintain the "preferred" set up for "most" of the racers in the day.