More or less.
Because I'm still a white westerner writing people from another culture in my own language. The unphysical stuff-- their reflex reactions, their motivations, to a very large extent the things I make them do-- will be what makes natural emotional sense to me. Much of what strikes me as significant or, well, striking, about these characters is stuff that a gaijin /would/ notice or value, and not necessarily what their author or same-language fans do. Even the writing shibboleths of In Character and OOC depend on a western interpetation of what these guys are all about, not a Japanese one. Arguably I've already interpreted the characters as westerners just by virtue of being a westerner reading them with my default and unnoticed cultural assumptions.
You need only look at some LotR or Harry Potter doujinshi to see the mindset working in the opposite direction. (Default Aragorn x Boromir? Wut?) (No, that's a joke. But still.) 'I don't think they quite get it'/ 'This is on crack' is a process that works both ways.
There's room for an argument that there's actually no need to get it, here in the fannish sandbox. The Japanese have fun with our movies, we have fun with their anime, no harm no foul. It may just be me who gets a little twitchy at the assertion 'I'm an American. I can only understand things as an American does' which was delivered to me a while back and that still makes me grimace years later. 'I can never truly see from inside the other culture' is a fact. 'I can only see from inside my own culture' may be the logical corollary. 'I have no need to *try* to see except through my preferred pair of cultural glasses' is what grates.
If only because 'American' is not a cultural monolith even in America. Much less in hyphenated Up Here where indeed you situate yourself in terms of where your family came from, even if family in this case is ancestors. It may have been a century since you arrived on these shores but that makes no difference. (It is a century since we arrived on these shores and it makes no difference. The fourth generation still goes back to visit its French cousins on a regular basis.) There are umpteen varieties of American and they live in quite different worlds than the Hollywood movie/ New York TV media default. You better be able to look outside your familiar cultural defaults or else you won't be able to talk to your neighbours.