I've read more into the batch sparging methods and I'm wondering if the amount of sparge water vs strike water has a key role in determining the efficiency? You mention 50/50 split, which would be a thick mash but lots of sparge to rinse the grains. I read on other forums people also use only 1-2 gallons to sparge with a thinner mash.
More reading to do
The 50-50 effect depends in part on the amount of grain. My grain bills typically are 10-13 pounds. I'll typically mash with 4 gallons of water, perhaps as much as 4.5 gallons.
Then sparge with 4 gallons for a total of 8-8.5 (though typically closer to 8).
I heat sparge water to 170; I've read enough that suggests heating isn't necessary, and I don't doubt that, but I'm taking 2nd runnings that are about 150 degrees and dumping them into the boil kettle, as opposed to what would otherwise be 50-70 degrees. Helps me get to a boil faste.
When all is said and done, I expect to pull off 6.5 gallons or a bit more. A 6.7 gallon yield is normal for me. In fact, I could get a bit more if I waited longer for the trickling sparge water to work through the grain, or if I salvaged the losses in the mash tun.