It appears that the overall yield / efficiency for the “Completed batch yields” report period is using the average of the batch percentages ? 
, but should probably be using the totals to compute this.
Otherwise, small batches, e.g. 50L batches on our tiny pilot kit, skew the number rather.
To clarify: This concerns the average shown with the totals at the bottom of these reports. The individual yield %age on each batch line is (of course) calculated correctly.