Note that Azure cloud portal authoritative DNS does
not support EDNS Client Subnet at the current time; it geo-locates based on the IP address that sends the query. So Azure will geo-locate any client using Google Public DNS at the nearest (by anycast distance) Google datacenter where the resolver sends queries to the authoritative DNS servers (you can see the entire list at
https://developers.google.com/speed/public-dns/faq#locations).
In your case, this will be Singapore; until Azure supported EDNS Client Subnet; there is little we can do to improve this situation, short of opening a Google datacenter in your country.