Hi OP, the attention you have paid to room acoustics is impressive. Most just add some treatment as an afterthought. Congratulations, however you seem a little unsure about it possibly being overdamped. May I suggest you, if haven’t already, download a free app REW and puchase an appropriate microphone.
There is a whole forum dedicated to REW and how to use it. This will allow you to measure your room and get a visual of just how the room is performing. For every size of room there is a target response to aim for which is the amount of time it takes for the sound to decay by 60dB known as T60, probably about 400ms in your size room.
Less than this time means the room is overdamped, longer means underdamped and so removes any guesswork regarding the effectiveness of your existing treatment.
The program displays the results on a screen showing problem areas, for example any peak or dips (nulls). This is presented as a waterfall plot where you can clearly identify the troublesome areas. I have found this approach to optimising a room the only way to go. That is not to say that your room does not conform to this standard but it is certainly peace of mind knowing that the room is correct. It will help positioning your speakers and also where to place any subs you may add.
There is also HolmImpulse (free) and what I use, Omnimic from Parts Express about $300. Consider that should you change speaker position or add/remove furniture a quick measurement will display the results.
It has been stated that the treatment should be adjusted according to the size of the speakers. This indicates a misunderstanding of the science behind this optimisation. It’s the room that is being treated and when correct it’s correct for all and any speakers.