Ideally you should keep in mind that many things change, once you know the specific acoustic characteristics of your room. As an example, you may have read it's beneficial to overlap the mains and the subs. If you have just one sub, that means you are now combining 3 sources, which can smooth the response in the overlap region. The benefit of doing so is quite specific. That means it's only a good idea in the precise instance where it provides the intended benefit. Otherwise, there is no benefit and at the same time, you have added a bottleneck in terms of headroom.
Another example is the Harman configuration. It works well based on the chosen assumptions involved in the original study. They were looking for the greatest consistency over means seats in a multi-row rectangular room. However, when I work with clients and ask about their seating arrangements, quite often they want to focus on one or two prime seats. If they can get a good result with one or two subs in practical locations, they are often happy with that. With this in mind, actual tests in the room often lead to other sub positions working better than front and back midwall positions. It's not a problem with the Harman paper but rather the reality involved in applying one configuration to a specific room with different priorities and conditions.
Typically you won't run the subs higher than 80 Hz, so the benefits of multiple subs are confined to two octaves. The actual experience is greater than this implies. If the bass is right, everything else improves.
The low midrange region, from say 80 - 500 Hz is a separate consideration. Quite often studios have this region better under control, with a nearfield setup, some consideration given to boundary interference and treatment that is effective here. When I measure studios, the response is usually much flatter than you ever see in a listening room. Often things in a room, whether dedicated acoustic panels or furnishings, aren't very effective in this range.
Here, you aren't as free with placement as with subs. Maintaining a good relationship with the midrange along with a coherent stereo image is key. This will usually be the highest priority. It's a good idea to trial some different positions. See how they measure. See how this impacts the sound stage. It's a trial and error process. Once you've found the compromise you like best, it's then a matter of looking at treatment and calibration.
When you have a horn system with dramatic dynamic range capability, if you get these things wrong, it can fail in a big way. When you get to have a listening session and turn it up, a not quite right calibration can stick out and get ugly! But when you get it right and it all comes together, the experience goes to another level ... and you can get carried away, flying high as a kit in your own little musical experience ... then you hear a banging sound. It strikes you as startlingly realistic and life-like. For good reason - it's the police at the door!