David
I thikn that you will find the efficiency is affected by volume quite a bit, unless you still calculated it on 23L, even though you ended up with less. I calculate the loss in my kettle with me efficiency. For example, if I get 23L into my fermenter, my kettle has 2.5L deadspace, I calculate my efficiency on 25.5L. If you get say 1050 in 16L and that is 50%, if you add the 7L lost to trub in the kettle, all of a sudden you have 23L at 1050, and an efficiency somewhere around 72%. You still made that 23L of 1050 beer out of your grain, so I figure that is what you should base your efficiency on. If, however, you punched in your finished kettle volume, and you still end up with only 49%, you are a bit low. First AG is usually between 50-65%, I think my first was 62%. Anyway, 7L deadspace is alot for a mashtun. Do you mean that you got 7L less out that you put in? Grain usually soaks up about 1L per kg of grain, so factor this into your calculations (if beersmith already hasnt). Maybe if you batch sparge and mix it up really well, you may get slightly better efficiency, but for now, I would concentrate on sparging slowly, and see if you can reconfigure your set-up somehow to reduce the dead space in the mash tun, and maybe reduce the wort lost to trub at the end of the boil. A stainless scrubby put over your pick up tube may help, and make sure you whirlpool, then take the wort from the side, rather than the middle.
Sorry if this post is a bit all over the shop, I spent the day in the yard, instead of drinking beer!
All the best
Trent