FortiAnalyzer Report subnetting Problem

Hello,

I am trying to create a report about the used bandwidth of each vlan segment, I know I am going to use the dataset Subnet-Top-Subnets-By-App-Bandwidth. However, the result showed all network in /24 but actually some of my networks are in /16. I would like to know whether the function ip_subnet fixed the subnet mask to /24 or how can I select between 8/16/24/else?

Thanks!