The word su is karma-pravacanīya when used in the sense of respect, (when it means 'excellently').,
As सुसिक्तं भवता, सु स्तुतं भवता excellently sprinkled by your honor. Well praised by your honor. By not ष being an upasarga, it does not change the स into 8.3.65.
Why do we say 'when respect is meant'? Observe सुषिक्तं किं तवात्र has this your place been well sprinkled to-day.,