Prevailing wisdom is that stuff in between speakers is detrimental to sound quality, but expedient for set up, which is why it’s so common. Low as possible and behind the baffle plain of your speakers seem to be the goals. I’m actually planning a wider lower rack as well. The only personal anecdote I have is that when I removed the TV hung on the wall (another bad idea that is convenient) there was an undeniable increase in soundstage depth. Of course once I got a new TV it went right back, convenience over performance happens.
Are you looking at additional acoustic treatments as well?