Yes, that should be correct. In one of my special setups i got a wildcard-cert that was issued to root.mydomain.com but covered owa.mydomain.com for main owa usage. Therforce i had to msstd:root.mydomain.com as msstd.
if the cert is issued to owa.mydomain.com and my msstd:extern.fqnd is msstd:owa.mydomain.com(as displayed in outlook), then would the command be:
Set-OutlookProvider EXPR -Server $null -owa.mydomain.com msstd:owa.mydomain.com
Set-OutlookProvider WEB -Server $null -owa.mydomain.com msstd:owa.mydomain.com ?