It's not clear how the actual cost rates are calculated.
SAP S/4HANA Cloud
Reproducing the Issue
Calculate actual cost rate with App Actual Cost Rate Calculation - Cost Centers.
In S/4HANA Cloud system, it's not possible to define splitting method manually. The default splitting method is "Activity Quantity".
The calculation example for splitting method "Activity Quantity" could be found in below link (check the calculation for ROH Rule):
The default splitting structure setting in Cloud is pre-defined.
Please check below KBA for the detailed configuration:
2916489 - Splitting structures system default settings
Exception calculation method: if the cost element is not included into the splitting structure, the splitting will be done by equivalence numbers of activity types. In Cloud, the equivalence number is always 1. So the part of costs will be splitted equally to each activity types.
KSII, KSS2, actual price calculation, splitting method, OKES , KBA , CO-OM-ACT , Activity Types , How To