Just a few things that can dramatically affect hair volume IMO:
Hair type (how tight your curls are - do they tend to grow out or down?)
Amount and weight of the product left on the hair
The weight of the hair itself
To the first point, you have lovely curls that look springy in your sig pic, a great start
To the second point, you could try slightly cutting back on the amount of LI conditioner or styler you use, or try more light-weight LI products - it's obviously a balancing act to try and hit that "sweet spot" you're looking for btw. definition and volume. Also, mousse works well for some people, if you haven't already tried that.
To the third point, have you tried things like "plopping" w/a micro-fiber towel, or using a diffuser for drying your hair (upside down, for optimal volume), or the the "pixie method" of diffuse drying? Also, some people dry their hair with clips at the crown (while hair is wet) to create lift (more about an alternative to that annoying method below).
To the final point, about the weight of the hair itself: cutting the hair relieves the strands of length, and therefore weight. It results in curls that spring up more. Strategically cut layers that include the areas around the crown and of the hair framing the face can really help give a great sense of volume, plus it's a lot less of a hassle than that clipping method (clipping it up while it's wet).