IMHO, you really should be using a hydrometer. I bet you'll get different and more accurate results. I know I did. In exchange for accuracy, its much more of a pain in the dick than putting a couple drops in a refractometer.Brewersfriend is doing it. @Mrs. Valve took the gravity readings. The refractometer has been calibrated.
That level of efficiency isn’t uncommon for BIAB.
And 70-80 is pretty normal for AG. You lose some efficiency for BIAB, so I still say that's pretty high. Either you're a wizard or your numbers are off.