The establishment of coherent Bloch states in heavy Fermion materials involves entangling the f-spin degrees of freedom with those of the conduction electrons with corresponding change in the Fermi surface. Coherence only develops when excited crystal field levels become depopulated in heavy Fermions, intermediate valent materials belonging to a different regime of f-electron – conduction electron coupling. Kondo insulators are argued to be a particular instance of coherent behavior, with data from La₃Bi₄Pt₃ – Ce₃Bi₄Pt₃ alloys showing how coherence develops only at high Ce concentration.