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The VRX's hi/mid measured measured flat at 20'. Have no clue what it would do farther out.
If it's flat at 20' (for a pseudo-point source) the highs will start to fall off 'more' the further out you go, but the rate is fairly slow, something like a couple db per 100ft at 10KHz. Sound absorption in air is function of temp & humidity, and is frequency dependent.
I don't know how many VRX's were used, and how high they were flown, relative to 20', or how the array was tuned, but if the floor was flat and the speakers ground stacked, and if you can ignore reflections, you should expect the highs to fall off at the back of the room. Reflections will make response a lot more complicated.
Ever walk up to an outdoor concert? What's the first thing you hear from far away, the highs or the lows?