I can't say for sure, but it is definitely true that JAV actresses tend to have really great fake boobs compared to Western pornstars. Well, if that's even the right word here. The augmentation is usually a lot more subtly done.
^I've wondered the same thing. But I think Japanese women might genetically just have different looking tits. The fullness and firmness seems to be unique to them, I could be wrong I just think the jav girl tits have a different look to them.
That's my problem with western implants and enhancements: starlets don't let the breast recover and go back to shooting as soon as they get them done (maybe impatient to show them off or simply for the paycheck) ending up awful 99.9 % of the time. As a result I lose interest in them and don't watch their scenes after the surgery anymore. It was the case for Lana Roy for exemple, her tits don't suit her petite figure at all On the other hand Zafira's tits, which boobpedia state as enhanced (but I doubt it) are great, Silvia Saint I believe has implants but it's difficult to tell, unfortunately those are rare: to me good implants have to go unnoticed