Read the HBT post and came up with following factors:
A) Gravity readings
I have a cheap refractometer off Amazon, and it reads all over the place. I need to take about 8 samples then average them to get anywhere near what my hydrometer tells me, and still it can be off. Refractomers are finicky tools that need to be calibrated pretty much before every use. I also have a $300 digital model and it reads much closer, but still I tend to trust my good old fashioned hydrometer over both these gadgets. Your boil gravity was higher than predicted, this tells us perhaps that reading was wrong in the other direction. It isn't clear if the readings were all temperature corrected, or if the kettle was stirred. Stratification is a potential culprit here too.
B) Not as much boil off
Sounds like you boiled off less than expected? That would factor into it.
This dilution calculator is handy:
http://www.brewersfriend.com/dilution-and-boiloff-gravity-calculator/
In this case, the 'fermentor' mode was unaware of just how much losses you are giving over to hops absoroption and kettle dead space. This is something we want to add into the 'More...' section in the near future. We are currently implementing a feature that will allow for multiple equipment profiles, and this will be addressed soon after.
C) Definition of efficiency
Part of the issue is the definition of 'efficiency'. The recipe is set to batch size mode 'fermentor', this means efficiency is defined as 'brew house efficiency'. Sounds like you have 86% BHE dialed in from prior batches, but it is not clear if we agree on terminology. To clear that up, please see our FAQ on efficiency:
http://www.brewersfriend.com/faq/#recipes16
And see or FAQ on how we define 4 types of efficiency:
http://www.brewersfriend.com/faq/#recipes18
Next time:
To avoid variations in kettle dead space and hops absorption, try setting your recipe batch size mode to 'kettle', enter 86% kettle efficiency (or whatever your to the kettle efficiency is, usually ~5% higher than BHE) and pad the batch size up by your kettle dead space loss and hops absorption to get the correct amount in the fermentor at the end of the day. The water requirements section will help with that.
