Why does SPW change the length of the bulkhead? I would need to check a known penetration depth

It is possible to perform a verification calculation on a known penetration depth.
For this purpose, the FEM analysis method must be selected and the general FEM data set as specified below:
Automatic calculation of the penetration depth: No;
Initial penetration depth: coincides with the penetration depth to be verified;
Increase of the penetration depth: zero. Select the Apply command and carry out the calculation.