Inconsistant object thickness (sliced layers number vs. design)

[agifagif]

Describe the bug
Object total real thickness is is 5mm.
5mm is correctly displayed in the object dimensions (see print screen)
Once sliced the thickness is 4mm (20 layers of 0.2mm) (see print screen)
Of course printed object thickness is 4mm

Expected behavior
Sliced and printed thickness should be 5mm

** object files
Stage.zip

Screenshots