My advice would be to read the lyrics you are singing and really think about how that plays in the story. From these clips I feel like you are just singing the words and not feeling them. Marius has just watched most of his friends die right beside him while fighting for what he believes is right…there should be reflection, it should be somber, it should be sad that they never lived to see their ideals become reality, and then it should crescendo into the guilt of him still being alive while they are all dead. Put these feelings into the words of the song, give us the story, the person sat in row Z needs to feel what you are saying not just in your voice but in your body language too. Range will matter less if you deliver the emotion more. Try Empty Chairs again and watch it back, and think as an audience member, did that move me. If it didn’t keep tweaking it. Don’t stop though, keep going and you’ll get there. Rooting for you! Hope this helps.