Fujitsu ScanSnap N1800 Operator's Manual page 473

Figure 1
Control point for scan
Feed
direction
Multifeed detection by layer will often mis-detect very thick paper.
When scanning such documents, select [None] on the [Multifeed Setup] window.
Multifeed detection rate may decrease depending on the document condition.
Multifeed may not be detected for the top and bottom 25 mm of a document.
25 mm 25 mm
Front side
473
Page top
Page bottom
Center of paper