Rate Schedule not generating WP messages on components

Dear all,

I'm currently working on a POC for a french prospect where we think the best solution for them is to use rate schedule to manage their solution (instead of classical WO).

I've created some items and managed to generate MPS messages for finished good with the SC type. The items have a Bill Of Material defined, and I expect to have some needs generated by MRP calculation,  but unfortunately there's no messages on the low level items.

Since I'm not comfortable with the rate schedule (never used for demo), I would like to know if there's a specific parameter to be defined ?