Usually those knobs are added to compensate for when the speakers are very close to corners or walls, which would make the bassresponse you hear unrealistically loud, causing judgement errors etc.
Your speakers are pretty close to a corner/wall, so you could try if turning it down gives you a flatter image. But if you are used to your setup this way and your low end translates like you intend it to, I would probably just leave it like that.
Oh, and acoustic treatment is always a good idea! Imo the best investment you could make. At the very least you could consider basstrapping the 4 main corners of your room. You can make them yourself for a fraction of retailprice if you are able to find the right material for it (very important! The foamy pyramidstuff won't do!).
Also, it may be worth looking into the symmetry of your setup. Looking at that picture, the first thing I notice is that your setup is close to the left wall and corner, which will result in a louder bassresponse from your left speaker and earlier reflections from the left wall, ergo, an unbalanced stereo image. If you have the room for it, try moving your setup around a bit. You may be surprised by the improvements you get!
Here is the inevitable
link to some info about this subject. I have no connections to this site, but their explanations have been very clear and helpful to me when I built my own traps.