Can very slight sulfide/sepia toning improve shadow density and shadow separation?

In the many books I have read regarding toning and darkroom printing, I have never seen the experienced behavior mentioned (or I am forgetting).

I made some prints using Fomatone MG Glossy that I ended up lightly bleaching for 20 seconds in a dilute ferrocyanide bleach. Then toned in a sodium sulfide bath. The objective was to slightly colour the prints which this achieves. However, I noticed an additional benefit when comparing the toned prints to my untoned copies. The darkest shadows have better detail and structure that was not normally visible in normal lighting was slightly more visible. In fact the blacks seemed deeper and less "flat."

Additional bleaching of prints to be sepia toned would result in a lightening of the print, but I've never heard of it darkening shadows. I made several copies of this particular print so I don't think it is a fluke. Perhaps the brown, black of the toned print is darker to the eye than the green, black of the untoned print? Similar to how excessive toning in selenium causes a print to lighten due to the brown tones reflecting more light than black, just the inverse?

Adding sulfide to the sulfur can very well add optical density, especially in the shadows. After all, you end up with silver sulfide instead of just silver, and at high densities, the brown hue of the sulfide will simply add up to the already present (more neutral) density of the silver, resulting in a higher density. That density will have a brown hue to it, but the human eye is generally not very good at picking up hue variations at low light intensities.

Other than that, I think the effect depends on a host of factors, such as extent of bleaching, formulation of the toner, paper used, etc.

I've always just selectively bleached....à la Jay Dusard......and found it works like a charm.