Do you adjust your subwoofer

The science answer would refer you to Fletcher-Munson and Harman curves. The subjectivist says turn to where it sounds right for what you're listening to. The purist epoxies the level knob in place only after excruciating critical listening sessions with curated selections. At the end of the day, you'll set it where you like the best, and don't have to mess with it too often 

I have two SVS Ultra 13subs with upgraded plate amps and now I can control all the settings on the subs through the SVS DSP app on my smart phone My tower speakers have built-in powered subs also, I have my SVS subs crossed over at 40 hz and sub volume relatively low  Depending on what's playing on my streaming play list i will tweak the volume and crossover on the fly  It's so easy to return it back to the original settings 

Not all recordings seem to have the same bass level.  I mean, what seems right to me, for that material.  So I do change the volume.  It's a db scale on my remote app so within about a  3-5 db range I find seems "right" in 90% of recordings.  Others set and forget.  As far as locating the sub that's a multi-faceted solution.  I find I can locate the sub at around 78hz and above so there's that.  Volume less impacting to me/my set up.  

I use 3 SVS subs and actually control them by a second preamp. My musical tastes run the entire spectrum and recordings vary greatly. Seems that the newer music is recorded with much more emphasis on low frequencies. This has worked for me going on a decade now.

I use Svs 400 subs which are  sealed And very fast and articulate 

they have a verygood app you can adjust from your tablet or phone 

you didnot mention the frequency response of your speakers ,

for some movies or even music with poor recorded bass just turn up the volume  as needed ,you want your Bass to blend if your speaker says plus or minus 3db at say 

40 HZ add 10 db and then godown 1 db at a time ,you want to get the most out of the main speakers , to get good fill and still have seamless Bassfrom the sub.

you don’t want over lap ,that's why  +10 db is a good start ,and many mfg 

pare not accurate in their measurements ,there is no. standard on exactly wen the frequency starts rolling off ,many mfg are not totally truthful.

if you bought a much better sub you would hear much more articulation in the Bass notes. Sealed subs are faster then ported subs as well as more articulate .

look at JL audio fathom , Wilson ,Myself Svs 4000-SB , the Rel has a open passive radiator similar to a ported sub more boom ,