it is better if you create your new CIT under existing CIT, so you will inherit its propagation rules. anyway, if you choose not to, then you need to make sure there is "imapcted_by" link between your CI and the transaction. this is calculated link. if not, then you need to add triplet for it in the CIT manager.
please note that KPIs are propagated only during the creation of the link, so if you dont have "impacted_by" and you are adding the triplet AFTER the original link was already there, then KPI will not propagate. you will need to re-create the link and this time the KPI will propagate.
each link has different meaning (for example: composition means when source CI is deleted then target CI will be deleted too, or containment means ownership so the child will be part of downtime if defined on the parent CI). same for the direction of the link. bottom line - it depends on the use case. I am not sure I can help much here.