I have maggies and no rug behind them - any bipolar speaker should have a fair amount of diffusion behind it for best sound.
My "Persian" rug is not as large as I might like but has been in the family for 3 generations. If it extends beyond a line drawn between you and each speaker (a triangle) that should be fine.
For high freq.a, which are the issue here, you can just use ray tracing to analyze the room. More info is in the master Handbook of Acoustics, which every audiophile should read a couple of times...