Where did you find those numbers?
Assuming this is related to RF planning your wireless network, that is a profession by itself. I'd advise you to consult a specialist for proper planning of wireless networks. If you need more insight, there are two in-depth documents by Aruba: Indoor 802.11n Site Survey and Planning VRD and the RF Planning part of the Aruba 802.11ac Networks VRD. In addition to that, there is a lot of training available on vendor-neutral WiFi RF planning, and your voice vendor may have some guidelines as well for optimal operation of their equipment on the wireless network.