Unfortunately, the NPA is poorly taught... and underused. Just as with many proceedures in the EMT curriculum, talk all about it... very little of showing 'how to do it' in real life.
Many things I have learned over the years that class has not taught, allow me to regurgitate the info: Out of the many hundreds I have placed over my career, I prefer the NPA over the OPA by a long shot. In many folks, it will cure the "snoring" while they lay there unconscious.
I happen to use it for more diagnostic reasons, and the benefit is a more quiet and easier respiratory drive, and a great guide for suctioning with a french suction cath.
I don't like fingers near the mouth much, and rotating an airway blindly can cause more damage than good. A tongue depressor with the OPA is a godsend.
The trick to a good NPA insertion ( I does not matter which nare you choose ), just size it correctly for the pt.
Lube the outside with some Kentucky jelly....
Enter the nare of your choice literally going UP the nose about 1/2 - 1 inch.
Now.... this is where you need to pay attention to technique....
Keep the distal end medially ( towards the septum ), and increase the angle of the nose hose so it is about 90 degrees to the face ( you are aiming directly to the back of the head ). Use your other finger to push the tip of the nose upwards ( piggyface ).
Gently introduce the tube right in. If you want, you could rotate the tube back and forth no more than 15 degrees either way... its really not necessary to do more than that.
Just push it in as far as it will go, have not made a person gag yet.
Using this technique, you decrease your chances of meeting any resistance, and any damage to the inside nasal structures. ( you don't want a bloody nose.... bad stuff, and it looks awful. Which has happened twice to me... mainly because I used to big of a NPA ).
There is nothing wrong with trying one, then downsizing if needed.
Hope this helps... and if the pt resists you, they probably don't need it.... and now you have a great diagnostic AVPU report for the ED as well.
Good luck... and be safe