I guess I will chime in. There are several different things being talked about, Tallness function, Scale function, and more basically what scale of PFs to use for fake stone displacements/ or colors.
When sending input to the tallness and/or scale functions white equals 1 and black equals zero, so whatever gradation mask or altitude distribution mask or PF you feed in will alter the fake stones basic tallness or scale according to the whiteness level in the spot were that stone occurs. It you have a set of 1 meter scale fake stones originally and then feed the scale function input a 50 percent gray constant all the stones will now be half a meter. If you feed in a Pf the stones will vary between full 1 meter and zero or they could actually go greater or negative if you were to feed in unclamped values.
The other item being talked about is simply the colors and displacements applied to the fake stone surface input. The "feature" scale in a PF is the "average", the lead-in will be the largest massed or clumped areas, and the smallest sets the tiniest details . For a one meter stone I would usually choose average feature scale somewhat smaller than one meter. These are things you can easily see in the fractal previews just scale the window to a 1 meter or 3 meter area and see what results you get as you change the scales up and down, but stones may be very plain if the features are too big for them.
Separate from the PF scales is the amount of displacement set in the displacement tab of the PF. It should be chosen to be appropriate for the stones you are defining. A one meter stone may only need 0.3 of displacement or less. Different looks can be gotten with negative displacement. Leaving displacement at the default of 1 may be too much. Again you can quickly use the fractal or stone preview window to see if the displacement is ugly or too great or too small or causing spikes. And there are also the roughness and spike limit settings to work with as well as continue spike limit.
For a 0.2 size stone trying to use 1 meter displacement will most likely be way too much resulting in blown up or spiky stones.
