Problem in segmenting small hand bones

Hi! I am new here; also thak you for the support and the developement of Slicer: I am really enjoying it!
So my problem is with the segmentation of the scaphoid in the RMI.

It seems that, even if I am using the 1% size brush tool, I cannot get the precise shape of the scapoid section. What is also odd is that when I use the draw tool I can draw the exact shape of the bone but then the segmented area is always off (please see the pic attached).

Is that a problem of volumes?
What can I do to resolve this?

P.s. also there are any other ortho hand surgeon here?

Thank you

This section of the documentation explains why this happens and what you can do about it: Segment editor — 3D Slicer documentation