But at the power setting at short final the engine may not be developing enough power to spin even a fully-fine prop at 2400, so one has no way to set 2400 (one could if the governor lever was graduated in rpm but they aren't).
So don't set it at low power. Set it when you still have enough MP on to reach 2400 RPM. And leave it there. Then when you go to full throttle, the RPM will go to 2400 RPM. Works for me...