Lateral reflections near 60 degrees matter while front-rear reflections do little.

Evidence

If the direct sound arrives from 0° it is clear that reflections arriving from about 60° will have maximal effect, but there is a wide range of lateral angles over which reflected sounds will contribute to the illusion. In contrast, sounds arriving from close to the forward and rear direction will have little effect. — Toole, Floyd E, Sound reproduction- the acoustics and…, 700