the problem with your theory of your Singapore Lic which is I assume on a par with my Australian licence is even though your probably right it’s up to the interpretion of the police officer your dealing with . You can argue the point and end up back at the police station or pay a road side fine of 400 Bht ( that was the fine I was given away )
Remember to some your a cash cow .
Let your wife drive when you can is the advice I give myself .