I guess it takes experience to know these things.
/Salute
I generally like to leave a lot of ash in the fireplace, not just a bed, but I usually push it up to the sides of the fireplace, and really only scoop out enough to let about 2" airspace under the grate. If the coals block it, there is less air so the fire slows and produces less coals. That way it is self regulating.