The epidural you had, and as such the immobility, would have affected the baby being able to get into the optimum position for birth.
I didn't have an epidural or pain relief to speak of (gas - hah! does nothing at 9cm LOL) but towards the end was buggered and had given up so was on syntocin to assist with pushing stage. So I was in the dumbest of positions - on my back, legs in the air, no room for pelvis to open and no gravity to assist my posterior bubba. Still managed to get him out without assistance, so I can only IMAGINE how much easier even a difficult presentation would be with better positioning and a midwife's (rather than OB's) assistance.....

And ditto what everyone else has said (thanks for the info on posterior births Michael, the more I read puts my son's birth into an informed perspective).