+1 ... Tabac likes a lot of water, as do most tallow-based soaps. The Tabac shaving cream also likes to be well-hydrated, whether its used alone or in combo with the soap as a SuperLather.Tabac likes and needs water and can hold a lot of water so don't be bashful about it, add water. It will get very slick with enough water.
Personally, I like my Tabac lather to be sloppy-wet, so I keep adding water throughout the face-lathering process, re-wetting the brush 2 or 3 times before I'm done and let it sit on my whiskers for a few minutes. I wind up with a lather that doesn't look pretty, but the performance is legendary.