Recently...had slow, hung starts. Modulated, like you said you are. New guys couldn't start it.0, as they didn't have the finess, for getting it going. They wanted it by the book...on the white line!! Like a fadec start.
We found the seals on the pressure of fcu side were leaking (bypassing) a small amount of fuel. The boost pump volume and pressure was slightly reduced...so a "calibrated" start was not acheivable.