What's this based on? AFAIK, custom molded tips, should create a better seal than generic ear tips, but unless they're molded with optimal insertion depth for a

What's this based on? AFAIK, custom molded tips, should create a better seal than generic ear tips, but unless they're molded with optimal insertion depth for a given in-ear, they might change the perceived frequency response. Bearing in mind that the material of the tip also matters, one might not necessarily get an "improvement", but merely a change in sound signature and a more secure fit.