PC would argue that no matter how small the vertical increment is, unaided nature cannot make it. Only a Creator can lift nature up to the next plateau. The amount is to be determined by the geological record and biological experimentation. But there is no vertical radiation.
Vertical radiation is only by fiat creation.
A root-species may give rise to several species by horizontal radiation, through the process of the unraveling of gene potentialities or recombination. Horizontal radiation could account for much which now passes as evidence for the theory of evolution. The gaps in the geological record are gaps because vertical progress takes place only by creation.