I'm pretty sure we failed the corridors after the Lock like 5 times. That is why we killed a lot of mobs there so we eventually made HB max stage. For max HB stage u need to farm those corridors (they are not mentioned in your quote). However, if u get disconnected in that area, you get teleported to Oasis.
P.S. After Darion you go up the stairs, hit the Lock and you get teleported to the mobs u need to farm in order to increase the stage level. Keep in mind that you may need to do the process more than once.