Com'on. This is just a 60ppm change of the mod frequency from the nominal. How can it change the recycling cav length by more than a cm?
This describes how the desirable recycling cavity lengths are affected by the phase of the sidebands at non-resonant reflection of the arms.
If we believe these numbers, L_PRC = 6.7538 [m] and L_SRC = 5.39915 [m].
Compare them with the measured numbers
You should definitely run MIST to see what is the optimal length of the RCs, and what is the effect of the given length deviations.