Yes, but like the lower part of the firebed, it needs very hot air - which it gets from having some excess air coming up through the firebed.
Some stoves supply smaller amounts of over-fire air to help burn off the carbon monoxide gas produced, so that it's heat it not wasted. Either with a secondary air damper, which is usually mounted in the loading door, or an air bypass from below the firebed.
The depth not only adds more fuel to burn longer, think of it like layers of blanket that help slow the heat loss as the burning gases try to rise. That resistance to air and hot gases rushing through keeps that heat in the firebed longer to help burn the coal more efficiently.
The term "liner" often refers to the firepot or firebox having some type of liner to help retain heat in the firebed. Many coal stoves use fire bricks, or a one piece refractory liner for the firepot/firebox to further retain heat in the firebed. Or some, called "suspended pot" base burners, channel the hot exhaust down around the outsides of the firepot to help keep it extremely hot without need of a liner. Those all are, generally, the easiest stoves to maintain long burning coal fires.
Paul