Some pictures will help. A non-mixing fluid to fluid boundary may be called an interface or a free surface. However, an interface boundary in Fluent is a cell boundary where the two (or more) meshes don’t align. Without knowing whether you’re using the terms in the same way I am, and without knowing what you’re comparing I have no idea what you’ve done, whether it’s correct (in the software) or whether it replicates the paper.
To create a conformal boundary use Share Topology in SpaceClaim.