JX92S - cabinet damping affecting midrange?

[AntM]

I wonder if anyone has experience on the effect of cabinet damping on midrange performance?
I'm nearing the completion of a small JX92S design New Jordan JX92S mini-monitor design

I auditioned an initial prototype which was filled with lambswool, then later I added damping panels (bitumen+acoustic foam) to the walls, plus made a few other minor mods (e.g properly glueing the font and back panels to stiffen the cabinet and reduce leakage).

Following the changes, I noticed that the midrange seems a bit recessed and lacking in power- it is particularly noticeable on vocals.

Is it possible that the damping panels have affected the midrange? Or is it more likely that the poorly damped and sealed prototype was adding some midrange colouration?

So far I have not added baffle-step compensation.

Any thoughts/help would be greatly appreciated. It is very interesting how relatively minor changes to the box design can affect performance.