If you are flying the earlier aircraft .mdl with the new JVVC interior and aircraft.cfg, the tail wheel sink is due to the fact that the old model has different contact points from the new one that came with the V3 release.
This difference could also be caused by static pitch or other variables that differ between the old and new models.
You can adjust the contact point and correct the tail wheel height for this model, but this will raise the height of the tail wheel for the V3 airplanes. You are going to need to create two separate files...one for the old model setup, and one for the new V3 release from Visser/Jahn.