Unfortulately this formula brings me back to 'scenario B' in whicha single (total?) value is repeated, across all 4 dimensions, including time. There is no cumulation per se.
I'm begining to believe there's something wrong with model/joins. All the "ID_DIM_*" columns I use in the formulas belong to the fact table (they're the FOREIGN KEYS), should it be otherwise?
The model couldn't be simpler : one fact table that contains a couple of measures and FK to 4 dimensions, one entry per day, and per each dimension (for the days the project is active) in the fact table.