Experience seems to indicate that the effect of the inhauls is noticeable. In the right conditions: upwind 6-12 knots. In the middle of that range the sheet can be hauled in to as much as 18" form centerline, but 0" if well outside that range, or reaching or downwind. Some intermediate setting for the transitions at the low and high end of the range. Easy to jury rig with a loop of rope for testing.
However, nothing beats having a dedicated crew person (elf) doing the jib trim.

Like in this picture going on a close reach while reefed.