The reason some rise is recommended is more about evacuating co from smouldering pellets than the smoke. But getting rid of the smoke is nice as wellMaybe a tiny amount, enough to keep it from smoking up your abode, but not much more. A 3" diameter exhaust pipe even if super hot won't create enough draft to pull anything much. hell, I have a 21 foot vertical rise of 4" and the pull is negligible at best. Won't even extinguish a match held in the bottom of the cleanout tee. You always need the combustion fan to work for you to roast biomass. To think you don't is false, because you do.
Like I said, in a power outage it will (maybe pull the smoke out but not any more) never tested that scenario because I have a diesel standby so when (not if) the power fails, I'm on standby in 45 seconds.