Previously, IIRC the AICS (Air Intake Control System) was inhibited on GR1 after all the bits were put under the nose. These bits disturbed the airflow and imposed some limits. As F3s needed AICS, and GR1s didn't, I believe most were removed from GR1s to stock up the F3s.
But that was 10+ yrs ago. and the GR4 may be quite different in that respect.
sw