I believe his work with Montserrat caballe made his voice... evolve.
In the upper range, he's using his headvoice with less chest resonance, that's like... 80 or 85% head resonances and 20 or 15% chest resonance, instead of the, perhaps, 75% head resonace, he's using
Those notes above High C sounds more brilliant, and clear than ever. His upper range from Barcelona on (The Miracle, Innuendo and some stuff from MIH) sounds better than ever. It's like he developed more control of the high register.