Maybe this will make it more clear,

this shows that if it was really 20cm scan height, you would get more scan data of the top of the object, and can be scanned in 1 scan



But because the true scan height is only 16cm (the software also cuts off a section of the bottom)
you must do a continue scan, and san the object more then 2 times to get the total data.



it is true a lot of devices have a maximum "work" size, and I know you can not always push to use this exact size envelope,
but being already at least 3cm smaller then advertised is just misleading !