What about current subwoofer setting:
Low pass 70 Hz & Volume 50?
Increase / Decrease?
May I suggest to take the measurement of sub only up to 100Hz and then the main LF up to 200Hz and main RT up to 200Hz.
Then increase volume and check distortion.
when your main start to have above 1-5% THD (80-90Hz?? .. for a midbass) you can start to enter with sub.
filter type is very important as well as phase. Start with 24dB LR, you need to have both main and sub filtered to avoid null/peaks.
to me this part is missing in the description of your system: crossover type low pass high pass. Try to have same distance between mains (LF RT) and sub vs listening position to avoid need of delays.
secondly I would be very interested in step responce 0-10ms. Try to have no reflection peaks in that time zone below 10-15dB (ideal 20dB) from first arrival to improve clarity and soundstage.
if you post rew file I can help.
best
Lorenzo