Just checked Ctein Post Exposure, page 69, figures 6-14, 6-15 and 6-16 illustrate that he tested and graphed the different curves that correspond to Condenser vs. Diffusion enlarger - after matching the prints for contrast.

It corroborates what Cliveh has been saying: The highlights have more contrast in a Condenser - even when the prints are contrast-matched.

Ctein complains that Callier didn't study photographic materials so it can't rightly be called the Callier effect. So we need a new name, I vote to call it the Collier effect and say George came up with it.