Hi Seyi,
Structure of your report is a bit confusing for me.Going by the report, you are trying to give a dropdown based on on Reviewer property of the Cost Center dimension for all the cells from L001.
If the idea is to give a dropdown, you can refer to a single cell instead of multiple ones as defined in your report. I have attached a screenshot for this.There are more than 20 values.
Alternatively if the idea is to populate reviewer for all the lines, then you can use EPMMemberproperty function in your report.
Hope this was useful.
Regards,
Varsha.