Thanks. I imagine I should turn off the other sub I am not testing right?
NO! You need to know the total summed output, at all listening positions, of any woofer producing an LFE channel or tower speaker run full range.
The room is simply in control of what bass you can hear, both when and where with in a room. It's just a matter of arranging enough subwoofers around the listening positions to ensure every seat, can hear every note, at the desired SPL.
Peaks can be dialed out with DSP, where dips should have their wavelength calculated so you can determine where a subwoofer should be moved so that 'dipped' frequency is no longer cancelled out.
Of course that could mean the new subwoofer location produces more peak(s). Again, the room is in control, so you just have to continue to work around it with more DSP filters, or potentially bass trapping in a variety of ways that suits budget/style.
You can actually predict the frequencies that are likely to have a peak or a dip, based on the dimensions of your room.