Thank you. I think I understand the difference now. I think opera singing is relatively open and relaxed, it has to be for the musculature to produce rapid and virtuosic effects, but covering (voluntarily partially tightening parts of it to alter it) produces distinctive overtones. (This is true for all voices, not just female).

Music, vocal and instrumental that is electronically processed and amplified loses a lot of harmonics/and/or overtones, that is why aficionadoes don't care for it. But you can get used to anything.