If you are significantly filling behind a wall, you should not be using a tiedback wall design.
Tiebacks are stressed using a center-hole, hydraulic jack with a calibrated pressure guage and sometimes a load cell. The tiebacks are not supposed to be stressed by movement of the wall when backfilling.
It is also a very bad idea to place backfill over a bar tendon. This can cause bending of the tieback bar tendon which adds a stress for which the tendon was not designed and which can cause tendon failure. If too much fill is placed before the tieback anchors are installed and stressed, the sheet pile wall will move forward excessively. If the tiebacks are stressed before
If neither you nor the contractor know the answer to the question, then neither of you should be designing or building the wall. You should have an engineer and a contractor who are experienced with tiedback walls.