More experimentation.
Lessons learned:
-KPW has a deep, dark, secret. It modifies the built-in fonts with stylesheets and messes with the line gap.
-KPW will not display custom kerning on custom fonts in AWZ3 formatted books.
-It is a PITA to fiddle repeatedly with individual glyph spacing to improvise what kerning would do more elegantly
I have taken the extracted Caecilia fonts, added weight to them, auto-spaced the glyphs, and then modified individual glyph spacing (ie. w, v, m, n, r, i, f, y) to produce improved fonts for my reading preferences.
Legend:
Caecilia_Size2.png = built-in KPW Caecilia font displayed with secret styling
CaeciliaExtracted_Size2.png = unmodified Caecilia font displayed without secret stying
CaeciliaModified_Size2.png, CaeciliaModified_Size3.png & CaeciliaModified_Size5.png are all screenshots of my modified fonts.
Of particular note, CaeciliaModified at size 3 shows the same amount of words as the built-in Caecilia at size 2.