iRule to provide alternate DNS CNAME response based on geolocation of Requestor

I have created a WideIP for testing.siterequest.com and want to be able to respond to a DNS request for this host with one of two CNAMEs based on geolocation.

If the source IP address is based in China, then I want to respond with cname.cncloud.com. Any other response should be to cname.cloud.com. The reason for doing this is based upon the fact that we use a specific CDN provider within China to improve application performance.

I attempted to use a simple iRule on the WideIP as below:

when DNS_REQUEST {
if { [whereis [IP::client_addr] country] equals "CN"} {
  cname cname.cncloud.com
  } else {
  cname cname.cloud.com
}
}

I have no default pool associated with the WideIP. Even from a host within China, all DNS responses return cname.cloud.com.

As an additional test, I created two pools and used the advanced settings to define a CNAME for each one. cloudcn_pool and cloud_pool.

The new irule is defined as such:

when DNS_REQUEST {
if { [whereis [IP::client_addr] country] equals "CN"} {
  pool cloudcn_pool
  } else {
  pool cloud_pool
  }
}

This iRule appears to have the desired effect, but there is one additional issue that is being reported. If a client performs a lookup directly against the DNS listener of one of my GTM devices, the lookup response is blank.

Through further testing, it appears that this blank response ONLY occurs when using a Microsoft OS and the nslookup command.

What am I missing? Is there a better way to do what I am trying to do?