exactly in accord with my experience.
with a "flat" F. R. (as per Audyssey or my old Technics SH8000 sig. gen/SPL meter)I found out i was missing quite a lot of very low frequency signals, mainly in movies and in some music.
i increased the sub output in steps of 0.5 dB until i felt it was good. then i checked with the ring drop in LOTR Extended Blu-ray, starting again from flat, and came to use the same vol. increase for the sub: +3 dB re. flat config.
so far, i've used this setting with a few bass heavy movies played at Reference Level, and have had no problem at all, most probably because my room is small (around 1300 cu. ft.) and the gain used in the sub is low, which gives it a lot of headroom.
