Even when sparging with correct volumes, I was regularly getting only 55-60% extraction efficiency on my first half-dozen all-grain batches. After looking at all other factors, including my crush (I crush my own), and water profile, and stirring during the mash, simply recirculating my entire first runnings 2 or 3 times bumped my efficiency up to 70%. Also making sure to get my sparge water hot enough - my larger MLT soaks up a significant amount of heat.
I mash in a large rectangular cooler (I think 60-qt. w/stainless braid manifold), and batch sparge and wonder if my MLT geometry is a factor. My grain bed is thick enough by most accounts (> 4 inches deep), but position and size of my manifold may be a factor.