The extended mash time (including the extra 35-40 Minutes) could have increased efficiency. If you are having your grains crushed by your HBS, then they may have adjusted their gap setting. If you are milling your own grain, then gap setting is something to look into if you are concerned with efficiency.
Personally, I have been brewing for about 3 years, and all grain for over 2, and as soon as I purchased my own grain mill my efficiency jumped over 10%. I am getting between 79-82+% depending on mash thickness and other factors.
An efficiency of 79% is really good. I would say 85% would be the max to shoot for IMO. Wort quality is an important factor when discussing BHE.
Good Job on your improved efficiency, I would recommend improving your process (which can also improve efficiency) rather than focusing on saving a couple cents by improving efficiency.