2 * sqrt(14 * (1/2)^2) = 3.75" not 9"
Not sure where that 9" midrange area came from, but whoever came up with that is bad at math.
Used to have 90db/watt speakers being driven by a 50 watt Sugden with a lot of headroom. Those speakers had dual-8" woofers and my room was similar to Miller's but lower ceilings 7.5-8'. Never had any issue "shaking the walls" or reaching listening levels beyond what most would enjoy.