It's definitely not all assigned to Singapore or to ap-southwest-1, the ip-range...

It's definitely not all assigned to Singapore or to ap-southwest-1, the ip-ranges.json file reports assignments to other regions, i.e.

3.0.0.0/15 ap-southeast-1 EC2 (Singapore) 3.8.0.0/14 eu-west-2 EC2 3.16.0.0/14 us-east-2 EC2 3.40.0.0/14 eu-west-1 EC2 3.80.0.0/12 us-east-1 EC2 3.104.0.0/14 ap-southeast-2 EC2 3.112.0.0/14 ap-northeast-1 EC2 3.120.0.0/14 eu-central-1 EC2