Tesselation limit ?

I know Tessellation Multiplier has a hard limit of 8.0.
However, some meshes seems to stop tessellating at much lower values.

Here’s the M_TessellationMultiplier material that comes in the ContentExamples project :

As you can see there’s no difference between a value of 0.2 and a value of 8.0.

Is this the expected behaviour ?
Is there any workaround to get better subdivisions ?