You are almost correct. The "propagation" has 2 pieces to it:
1) KPI propagation - this means which KPI type needs to be created on the Parent CI, based on child KPIs. This also determines which business rule will be assigned to the parent KPI
2) Status propagation - this means how to calculate the status on the parent KPI based on its children KPIs. this is determined only by the business rule of the parent KPI.
You probably used "Worst status rule" on the parent KPI. this rule is OOTB and will calculate the worst status of all children KPIs which are the SAME TYPE of the parent KPI. This is the reason you dont get status on the parent, because none of its children have KPI type B.
You will need to create Groovy Rule (a.k.a Rules API) and assign it on the parent in your propagation rule. This groovy rule will take the children KPIs of type A and do some calculation on them.
My guess is that you are coming from OM world and Service Trees/service navigator. The concept of status propagation in BSM is different.