ApexSQL Manage Inventory Scan, Different Subnets

Attempting to use a trial of ApexSQL Manage to run an inventory scan, but am not getting any results.

If I run a similar scan (nmap) from the same workstation, I can find several dozen MSSQL instances.  However, ApexSQL Manage does not see them.

I question whether it is something to do with particular subnet configurations.  For example, workstation is something like 172.20.75.x/24, but wanting to scan something like 172.20.0.0/16.

I've tried just about every combination of scan options, including "Domain", "IP", "WMI", "SCM", and "SSRP".

Anyone have any ideas?

Thanks in advance.