Likewise, fluxes supplied by materials like feldspar, whiting, dolomite, wollastonite, and talc are not going to be nearly as fluid as those supplied by a body frit. If we examine the individual materials from which bodies are made, we can see echoes of these same variables. A bentonite and a stoneware clay are good examples. Bentonite particles can be 100 times smaller, thus they are much more reactive in the kiln. Flint is available in a wide variety of particle sizes.
British kaolins are much more reactive than American ones.
In summary, you can probably see that predicting body expansion using the same calculation techniques as for glazes is a little misguided. Expansion is not a product of the mere presence of molecule types in certain proportions, but is determined by the form in which they are added and the extent to which that form allows them to interact and form a glass network. Differences in particle size, mineralogy, and firing profoundly affect a bodies expansion in ways that standard ceramic calculations cannot account for. Before finishing up with the topic of glaze fit, I'd like to explain a practical glaze-fitting method used in industry that lends itself well to inexpensive adaptation. This involved taking an existing transparent recipe and increasing soda and potash while cutting the SiO2 and Al2O3 as much as possible.