Record yourself and your friends speaking words with initial schwa (but not before velars) and final schwa (e.g., "annoy," "obtain," versus "China," "sofa"). Find at least 10 different words (5 each) and at least 6 speakers. Then check to see whether your speakers use a lower schwa in final position than in initial position. You can use speech analysis software to help if you're not sure. Are they consistent, or do some speakers switch from one vowel to the other?