Topology issue in gtm

Gtm has pool set with below pool members

Server A from London A area

Server B from London B area

Server A from Singapore A area

Server B from Singapore B area

Server A from US A area

Server B from US. B area

LB method set to topology

Client from London when tries to access gtm url , it toggles between 2 London servers.

The expectation from the london client is that everytime only (server A from London) should be resolved by gtm.

Could someone please advise... Thanks!