@hilde45 : With respect to your bass issues you are presently seeing on your room sweeps, I guess I'd just say two things:
First, any data must be quite specific (frequency, +-db, left speaker or right speaker, mic placement, listening position in relation to speakers and in relation to room length, and show graphs/waterfall). Also, I'm assuming you have no corner or front-wall bass traps in place yet? If you have traps in place, what are they and where they are helps to answer specific questions. You won't get much good advice with such a general question. The second thing is partially addressed above: where is the listening position in relation to the front wall (and to the speakers). At 6.5' from the front wall, I'd assume you are likely 13-15 feet from the front wall. That would position you at half-way between the front and rear(?). Or, are you already at the standard 38% recommended to avoid nulls. No modes on your sweeps?
If what you are seeing on the sweeps before treating is just a couple of nulls, that's exceptional. Treating is easy at that point.
Are you measuring each speaker separately? Do they some very close graphs/issues?
Just a general response to a general issue is, bass traps/corner traps can be the product of known specific concerns. It is pretty straight forward. However, generally, a corner unit should be 34" wide for effectiveness, and maybe floor to ceiling, maybe not. They usually won't cure the problems by themselves.
You can reach out to the acoustics thread at Gearslutz forum if you provide pretty specific data - only then would you get good advice, including type and placement of LF treatment. You can also tap into some great guys who have tested, built, installed treatment professionally. But, you have to have all your data (room dimensions, speaker/listening locations, room sweep data).