Ldap parameters to search in specific OUs

Hi Guys,
SM 9.52.

We are service provider company & we have multi-tenant environment.

We have integrated SM with Multiple LDAP ( each one for a specific client). 

Now for this new client, his users are stored in different OUs under the root. So we had to put the root ldapserver1 in the sm.ini file. If we do so, whenever the user is logging to SM, it is taking like 20 seconds to login.

ldapserver1:IP89%"DC=domain,DC=com"

Is there another parameter that we can add in sm.ini where we can specify the OUs that need to be searched? 

Or in the ldapserver1, can we have it in a format that will search the specific OUs? (we have 4 OUs that are on the same level, & they all have users.)
for example ldapserver1: IP89%”OU1”,”OU2”,”OU3”,”OU4” 

does this work? has anyone tried this?

Please let me know.

Thanks