You have a very flat response. The person sitting where this reading was taken will not likely experience any boominess in the bass. In fact, they might think it needs a bit more bass.
This is not a phase issue. With a single sub, phase issues are a problem around the crossover region caused by an interaction with the mains speakers that are producing those same frequencies.. It can cause a dip or a peak at those frequencies. You don't have that problem.
What the problem might be is the differences between different seating positions.
To establish this, take response checks at various seats and see if there is a peak that causes the boom. Many people adjust their filters to average a good response over a wide area, rather than optimizing a single area at the expense of all other positions..
brucek