I tend to stay in that tunnel as well. However, you've missed some vital points of the farm system there.
To begin with, unless you exit the tunnel or save/load you won't get orogs, but only dwarves which you get 13.000 exp for each.
Another good point is that if you're invisible they will zerg up at you. ADHD clean s the place pretty well and you'll be able to sum up a LOT of exp.
I tend to get 1-2 million xp per char before leaving the tunnel.