Can you supply a "geometrical" vision of your termed 'relative stasis' please?
As to "base rate", in terms of a any sequence of data collection and analysis, I know by experience there is a exploratory tendency, which admitted IS subjective, that tends to extrapolate from a local knowledge to larger regions but it seems to me that Mayr's insistence that Croizat "accept" the standard rates (or perhaps 'base rate' as you had it) was a wrong way to grow"" biological thought or simply an ad hominomen on how Croizat reasoned reverse wise from a global or pantropical distributions to local "endemisms" or Cain centers of origin. There could be a better logical rework of Croizat's corpus if one were to get beyond the mass matrix defintions of NZ panbiogeographers per track width which so far I assoicate univocally with two-way velocities FROM empty space for any local endemism but this is less biological than even physical chemists think so it is not quite delimited even if it is logical. I almost think that it is possible to consider stasis in terms of the geography of different chrophyll stacks(intraorganically) but that is quite an extreme kind of thought on the subject.