Chest:
This is ok. It is just some message to you. IE3D users the polygons and vertices to do the meshing. If you have 2 vertices close to each other, IE3D may create a cell with tiny area but not tiny length. To the extreme, such a cell may cause numerical instability. IE3D gives you a warning on small edges formed by 2 vertices. If the value between the sign "<" do not differ by an order of 3, you normallly don't need to worray bout. If the "a < b" and a is 3 order smaller than b, you may want to select NO and IE3D/MGRID will indicate where it happens and you may want to check why. In most cases, there might be accidentally some inserted vertex there. You just need to select them and remove them. Certainly, you can use ADV EDIT->REMOVE REDUNDANT VERTICES ON CURVATURE command to remove those unneccesary vertices to improve the meshing.
For your case, believe a is basically the size of your probe, and a is about the same as b. You don't need to worry about it. The value b is automatically determined. We just want to give you a warning on it so you understand there will be small cells created.
Best regards,