True envelopment needs reflections delayed beyond 80 ms, impossible in small rooms alone

Evidence

Here it is necessary to emphasize that reflections occurring in small rooms cannot alone generate a sense of true envelopment. Envelopment requires reflected sounds with delays longer than about 80 ms. These can only be supplied by recorded signals reproduced through multiple loudspeakers. — Toole, Floyd E, Sound reproduction- the acoustics and…, 729

Categorization

• DEFINE: Sets the operational definition of true envelopment: requires reflections with delays >80 ms, which small-room acoustics cannot provide naturally.
• QUESTION: Why 80 ms specifically? Worth checking whether this threshold maps to the precedence effect (Haas) or to the onset of perceived reverberance.