Sometimes when I am working in this new way I feel the voice becomes nasal… but then again, it might be that I am still not very familiar with the correct feeling. How can I tell the difference?

The feeling of being nasal is probably a good one. Most of us are not familiar with the sensation of resonance in that area so it can seem wrong. Good function does feel like we are singing through the face around the nose. Many have a habit of singing through the mouth with a lack of head/facial resonance. This feels like the tone is going through the bones instead of through the air of the mouth. So when you experience the sensation of tone in the bones of the face it can feel nasal or wrong. The best way to tell the difference is by how it sounds. If you record yourself check on how it sounds. The way you can tell by how it feels is an undesirable nasal tone feels tight or constricted in the nose. A good tone feels like it is all over the space above the mouth, as well as in the mouth and throat. A bad nasal tone needs to be pushed forward into the nose, a good one feels like it fills the spaces behind the nose. Pitch also has an influence on how this feels. On lower and middle pitches the resonance feels all over. As the pitch ascends we feel the resonance exist more in the upper pharynx and head, which sympathetically is felt in the face. But again, we don’t want to try and create this effect. It is a result of good, vibrant phonation and a good resonance form. An undesirable nasality is usually the result of trying to create this result, which causes muscles in the throat to constrict and restrict the resonance in the nose.