If you look below, a value of 0 makes the fire very sharp but small, as you adjust the value it becomes more bloated and looks more like a round circle rather than fire. Here you have flame size , this controls believe it or not, the size of the flames. Essentially the smaller the flames the more there are, but if they get too small they becoem like confetti and look very ugly. A safe value is anywhere between 10.0 and 35.0. The default value is 35.0.
Density controls how thick the fire is in a way, how transparent or dense the fire is.
But if it is too dense there will be colour bleeding because the inner colour will have higher majority over the outer colour. If you look below at the density values demonstrated. The default value is 15.0. Flame detail is similar to flame size, but is more designed for the edges, the values are limited from 0 to 10, and with a value of 0 it looks very round and blurry, with a value of 10 the edges are very detailed and crisp. The default value is 3.0.