Check your PVC and raise your resin solids a little. I have to run at both high pigment and high resin loadings, especially in small particle pigments. I get more than puffiness - it is actually like a marshmallow texture. Marshmallow is a good word. Marshmallow is nothing more than corn syrup and air.
Corn syrup flows.
Marshmallows do not. The air is the only difference. Your high resin solids are just like corn syrup. At the top of the mill, if there is air available, it will be whipped into the mix and produce a tough, stable, air emulsion, for the exposed discs are excellent air pumps and whippers. This is one of the real advantages of a sealed mill.