If the cowstics don't quite look right, you can try fiddling with the Object Radius parameter. Setting it to zero tells HD Caustics to measure the radius of the object for each point that's rendered. If you know the radius already, and it doesn't change much throughout the object, type it in to save some render time. This controls how quickly the object turns opaque as it gets thicker. This affects the shadows and the actual object.
Smaller values turn opaque faster than larger values.
To be exact, this is the thickness at which the color and transparency of the object will be equal to the settings in the Surface Editor. Usually, you can just use roughly the average thickness of the object. Or, you can try setting it to 0.0, which tells HD Caustics to ignore the thickness of the object, and to fake the thickness effect. This saves render time, though it may not be as pretty. Chromatic aberration causes the color of the cowstics to depend on the index of refraction.