Your lower efficiency was definitely affected by it being a bigger beer. For a constant pre-boil volume and process, lauter efficiency drops with increasing grain bill size. There is nothing you can do about this, except increase your pre-boil volume and boil-off, but it's still a hard slog to make up for the larger grain bill weight. For example if you compare a 10 lb grain bill vs. a 20 lb grain bill for a 5.5 gal post-boil volume, with 1 gal/hr boil-off. For the 10 lb grain bill, you need 6.5 gal pre-boil, and a one hour boil. To get the same lauter efficiency with the 20 lb grain bill, you would need 13 gal pre-boil, and 7.5 hours to boil off the 7.5 gal required to get down to 5.5 gal post-boil.
The chart below shows how lauter efficiency varies with grain bill weight to pre-boil volume ratio for no-sparge and batch sparge. A very well done fly sparge can get you 2-3 percentage point higher lauter efficiency than a 3X batch sparge @ 0.12 gal/lb grain absorption, but a poorly done fly sparge (with lots of channeling for example) can have lower lauter efficiency than a single batch sparge.
View attachment 593374
A braid pickup is not the optimal choice for fly sparging, and the larger diameter the MLT, the worse it will perform in general (has to do with flow length and resistance to get to the pickup.) For optimal fly sparge performance you want a false bottom, as this drops the flow resistance to the pickup to almost zero. So, the braid pickup may perform worse on your larger MLT.
To really understand what is happening, you need to measure your conversion efficiency (
use the method here), calculate your mash efficiency (using any of the on-line calculators), and then calculate your lauter efficiency as:
Lauter_Efficiency = Mash_Efficiency / Conversion_Efficiency
If your conversion efficiency is less than 90%, you need to work on that. Finer crush is the biggest help, and longer mash times are a distant second. Other variables like precise pH and temp control are much less important that crush and time (w.r.t. conversion efficiency.) If your lauter efficiency is not beating a single batch sparge, then you are better off batch sparging than fly sparging. Or, you could try to improve your fly sparge game.
Brew on