If low end frequency reflections off a wall from the rear are a problem a bass trap could help Take a look at a shotgun frequency pattern graph.
in addition, interference tube shotguns do not always work well in interiors, try a hyper-cardioid
It is a hyper so I am thinking must have been hard wall reflection.
For me these are difficult to get just right.
The location (a catholic church) has had many complaints from sound
guys and some with far many years than me so it might be "live with it"
when we record in a week from now.
A bass trap is a acoustical passive low frequency baffle which won't do much good in this situation.
Shotguns ARE interference tube mics. (numerous ports on the sides)
Hyper/super cardioids are Sennh. MKH-50, Shure SM-81, Okava-012, AT-453, Schoeps CM5s, ect. Mics like these may help but get the mic(s) as close to the sound source as possible to get the desired source / room balance. In any case, a camera mounted mic will not do it... from your description..