Using offset method ZOFFS gives inaccurate (stress) results.
E.g. Meshing a tube on the outer surface and offsetting it using ZOFFS to the midsurface position gives different result with meshing the tube directly at the midsurface height.
Solution
For the offset method ZOFFS it is recommended to have appropriate mesh size e.g. that it is fine enough. Because, the method will offset the element's position, but it does not adjust the (mass) properties of the elements. Otherwise the overlapping or gap between the elements will take toll to the accuracy of the result. We can try and put an extreme value of offset and display the mesh to depict the situation more clearly.
Notes