Shadowy gains different at different levels?

From Fallen London Wiki

Just noticed that my newest alt (shadowy of 79, or 100 modified) gets +4 CP shadowy in addition to the shadowy from the action itself from the 3-action casing options. I've tested this with all the 3-action choices except "Criminal Assistance" — I'm out of actions for now.

I'm not sure what the cut-off is. The +4 happened both before and after reaching master thief 5 / name whispered in darkness 5 and before and after reaching modified shadowy 100, but my other alt (shadowy of 160, or 198 modified, and tier-1 POSI) is only getting the +2. Maybe base shadowy 100 or POSI?