That effect is shown clearly in Hans Windisch's 1938 book
Originally Posted by Bob Carnie
"Die Neu Foto Schule" (also published in English as The New Photo School) where he recommends what is now known as the Windisch surface developer. In fact's an older formula which he doesn't claim as his own.
The principle is that a tanning developer hardens the emulsion proportionately to development so in areas of extreme exposure there's more hardening and less penetration of the developer,. This was very important with older thicker emulsions prior to the 60's some of which had poor antihalation backing and that halation was worse in the emulsion closest to the support.
Modern emulsions will exhibit a less marked effect and will vary depending on the emulsion & staining developer used.