You can transfer Amex Membership Rewards points to Singapore Air, but still, it's a lot more miles than United.
We have had guests fly to Raja Ampat from the East Coast US and found it was easier to come via Europe to Singapore and then take the onwards flights from there either via Jakarta or Manado to Sorong. Perhaps more miles but it was commented that the flight was less difficult and better connections.
Best wishes
Siren Fleet