Here are some old references and discussions on the forum of molds vs. domes, amount of venting, etc.
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A review: Article on open fit vs closed fit
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One of the original papers the review is based on: Article on open fit vs closed fit - #10 by jim_lewis
It’s a multi-dimensional problem. And as with many things, there is theory and then there is how well the theory is implemented in practice, e.g., if a good impression is not taken, you might get a lousy mold and so on and so forth.
Not everyone is happy with molds but my impression from skimming many posts of the forum is that most people are happier with them than with domes because they are a custom fit and you can design in, one way or the other, the amount of occlusion that makes you happy or not, and some HA’s, like the Signia that I think Sierra wore (whatever happened to him? hope he’s safe w.r.t. Covid-19!), have active cancellation to dial out the sound of your own voice yet maintain a fair amount of occlusion. So one has to find what works best for oneself.