Vertical splits are more common with pads than with sulphur caps. This is because of the initial stress distribution from the cap to the surface, and the fact that many surfaces do not meet the planeness requirements prior to capping.
Since break patterns cannot be conveniently duplicated, it is tough to get correlations. You would have to review hundreds of test results of the same mix in order to get something like that, preferably by the same operator to get consistency of the break description.