One of the bigger take-aways from Shady's article on
Speaker Grilles: On Or Off? had to do with speaker placement being a much more impactful variable on sound quality rather than whether you used grilles or not. IIRC, your placement had that entire cabinet surface top in front of your center channel. Soundwaves are coming out and some are bouncing off the baffle of the speaker itself: this is common and good speaker designers account for this in the XO designs. Longer waves come out from the drivers and should radiate freely into the space around them. What you have is a significant boundary where (lets arbitrarily assign 40% just to help illustrate the issue) 40% of the soundwaves from your center speaker are being forced up and away from your listening position. Some of these may interact destructively with other soundwaves emanating from your Center creating cancellations, while others are sent bouncing haphazardly around the room.
Simply tipping the speaker up an an angle, say, or elevating it completely above that surface may or may not change anything. The better strategy is to have the front baffle sticking out just a little bit in front of the cabinets, and doing so in a way that has the speaker aimed more directly at your LP. The best strategy is to have the Center on its own stand which will allow it room behind (assuming it's ported) and room all around such that the speaker will perform as designed, radiating soundwaves naturally into your room and directed at you.
There is a lot of discussion in that thread itself, but reading Shady's article, and watching
Gene's subsequesnt video may help your understanding.
Please mind, we all are questing for the best acoustic experience we can. It is your system and home, of course. Another topic that may or may not come up for you though, is if your center channel ever underperforms in HT application: unintelligible dialog being the worst. This comes up a lot on the forum here, unfortunately. And the solution is often times placement related.
Cheers!