Efficiency discrepancy

I think that the issue is how both are calculated.

http://www.brewersfriend.com/brewhouse-efficiency/ is not accounting for losses in your equipment while beersmith is accounting for losses.

I think if you took out the losses in beersmith, you would get the same efficiency as brewersfriend.

Gauging efficiency with 100% accuracy is not something you can really do from one brew to the next. You should certainly pay attention to it, and make small adjustments accordingly. Over time, you'll be able to accurately predict efficiency with your system for a specific recipe. Even then, there are some variables you don't have as much control over; water quality, ambient temperatures, humidity, etc. Even with the same recipe, sourced from the same ingredients, you can have some variance.

For example, I started assuming the standard 70% and for the most part, my brews were within acceptable differences, but because I keep meticulous records, I now know that I can reliably hit about 74% for most standard beers, ~70% for 50% wheat or very strong beers and 78% for session beers. I use kind of a goofy method to determine mash thickness, which plays a significant part, but I generally keep it between 1.5 and 2.0 qt/lb. When I create or modify a recipe for my system, I take that all that into account and can generally predict fairly closely the anticipated efficiency.

Mash efficiency calculators are just an estimate based on an average yield on a specific grain.

They have a really wide range of results because they assume a perfect mash, with ideal crush, ph, water grain ratio, lauter technic etc. Once your brewhouse effeciency % is determined if those variables change your % will change.

To do it right they really need to factor mash thickness, ph, lauter details but I've not seen a calc tackle this yet.

More importantly grain harvests have different potentials* You need to update the potentials for each grain from the data sheet from your specific grain lots provided by the maltser. But this information is usually lost unless you buy by the bulk sack 50-55lb to get the lot # and look it up.

Mash ph plays such a big role in effeciency, your effeciency can be drastically different from batch to batch just from inconsistency in filtered tap water. Just one of the reasons to build water profiles from RO.

I do BIAB and my efficiency has varied around 70% from 65% to 75%. I've found that something as simple as stirring my mash 3 times in the 60 minute rest and not stirring it can affect that number greatly. You're outside of the realms of common efficiencies in what you're doing. Certainly I know of people using Beersmith who have efficiencies into the 80's.

"... so far above an efficiency that BeerSmith is aware of"

I'm not exactly sure what you mean by this, I'm positive BeerSmith is aware of efficiencies above 73%.

It's very common to get higher efficiency on low-alcohol beers with smaller mashes since you're running proportionally more sparge water through each unit of volume of the mash bed, giving more opportunity for trapped extract to be leached out and recovered.

It's also not uncommon to see a fluctuation of ~5% efficiency between batches of the same beer, stemming from small differences in equipment setup and process. Do you have any other records of your efficiency or are these the first ones? It could just be the combination of a smaller mash coupled with a slightly more effective runoff.