On an infinitely large plane or in an anechoic environment, neither of which applies to real listening rooms.
If real rooms were uniform diffuse fields from reverberation the SPL would not drop over 3dB once you got past the critical distance. Unfortunately they are not.
A 3dB/distance doubling draw down rate is typical once moving past the 'critical distance' (since real rooms aren't uniform diffuse fields, the term isn't accurate in this context).
Critical distance is about the reverberant field or may be also considered the signal to noise ratio back there. If the impulse response is the measured level then critical distance does not apply. The method and values given are for basic calculations only and should have said that. Signal SPL will always be at least as loud as shown by the method which is very useful for determining the assured minimum level achievable. As you state back in the reverberant field things are much more complex with a music signal. I got more that he was looking for the minimum level from the impulse by the way the discussion has been framed so... we are both right.
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