Re. the calculation of efficiency, looking at the formula I would guess it has something to do with the way HRA is calculated? But that's just science and mathematics.

The shared wisdom in this thread offers us three alternative explanations :

1) "it's just a display issue, will be fixed soon" (tm)

2) the asic farmer has left the building, resulting in mo' moneyz fo' us

3) he who has true faith in the rock, may become super-efficient.