I know training doctrine in PA (from about 5 yrs ago) was changed from waiting for negotiators to show up (Columbine rules) to having the first four officers form a fire team and go in. Training included clearing rooms with front two or three while having rear guard watch your 6, also transitioning intersections with left and right guy covering sides so lead could cover ahead without having to cover his flanks too.
That number seems quite prudent, especially with the tasks as mentioned. Thanks for the mention.