Tuning Rel G1

I use a test CD for tone generation to see where my main speakers start to seriously drop off at the low end, and adjust my REL to pick up the "Bass Ball" at what seems to be the point where it meshes with the mains. "Mains Meshing" is the proper audio term I just made up, and the volume level can generally remain where it is until I need to tweak it due to a lack of or overabundance of bass. Although my main's specs allege they work down to 32hz (if nearly inaudible minus 10 db or something counts, I suppose they do), I found this to be nonsense so the sub kicks in at maybe 52-ish and is capable (according to the test CD) of making useful bass to around 23hz or so. It sounds great.

01-09-15: Trcns
I dropped the Crossover from 35 to 25 and then even to 20 hz and started to increase it little by little. At 20 to 25 Hz I had to increase the volume from 6 to 9 but after 25 I had to go back to 6 otherwise the bass was too high.

This is the point where the sub adds to what your speakers can do. IMO this is also the perfect spot to make sure your phase/timing is correct (neither leading or lagging the main speakers).

At 40 Hz sound stage does improve as compared to at 25Hz. There are some songs which have more bass than the others but overall the result is pretty good.

Yes the sub is adding to the soundstage because it is crossing into the frequency range your main speakers already do. You have found some tracks with bass that seems too much because you are adding is there.

That said as my speakers are breaking in the bass is getting a lot deeper. My speakers are rated 40hz to 50khz. I initially I had my sub set to 36hz. Sounded pretty good until the lows opened and tightened up. With certain songs the bass is too heavy. So I have since went back on the crossover setting to 28hz just so I am only adding what the speakers can't do. Whats pretty amazing is I only have about a dozen songs where I can hear when the sub kicks in.
Just my opinion and my preference. Glad you have it setup they way you like it because in the end that's all that matters. So if you ever decide you too much bass for certain songs you can always re-adjust back.

The reason I stuck a "chicken head" knob on the level pot of my REL is simply because it makes it easier to see and feel the knob for adjustment. Unless you use some sort of digital nanny circuit DSP filter, you should want to adjust this thing when bass overwhelms things or personal taste demands more bass. It's easy, and puts you in the tone driver's seat.