I'm no superstar when it comes to singing, but one or two points that have helped me in the past might be worth consideration.

There is a big difference between belting it out at a session or floor spot and singing into a voice recorder at home (or even in a studio). For one thing, the ear of the beholder (beerholder?) is far more selective than the diaphragm of a microphone.

Many performers on recordings give the impression that they are "holding back", maybe thinking (or not thinking???)too much about what they are doing, consequently losing the spontaneity of the occasion and quality that their natural vocal achieves in a live situation.

Again, in a recording situation, many singers read the words, or, at least, use "cheat sheets" and don't know some of the songs really well. A better result might be obtained from learning the words off by heart before recording, giving the singer more confidence, and then projecting to an (imaginary) audience as if it were a live performance.

Phil, please accept my 10p worth in the spirit in which it is offered. And if you don't believe that anything I have written applies to you, then please feel free to ignore it. Might be useful to a few others in this place, though.....   :-)