Konica Minolta Fujitsu Scanner - Manual (Page 298)

●AP-4
- The deviation in the amount of the light transmitted through background areas
must not be less than 10%.
HINT
The type and the conditions of document and the conditions sometimes
cause the double-feed detection rate to drop.
HINT
When the overlapping check is specified, the paper sheets which contact
closely each other, such as electro-statically charged paper, can result in the
miss-detection of double-feed.