On some redesigned female armor I see plackart designed as V-shaped (for example gingerhaze’s purple-white-pink platemail, recently featured at BABD). It looks better aesthetically but on historical armor I saw plackart designed as upside-down V-shaped (for example look at wikipedia article about plackart). I wonder if straight V-shaped plackart which I see a lot in fictional armor has same functionality as a historical prototype.

Frankly, I have no idea about significance of V-shape in regards of realistic plate armor (all I learned about armor design was through running this blog). Seems like your question is more suited for an armorer, like Ryan ‘Jabberwock’ who wrote this article.

What’s significant in the post you’re referring to is this bit gingerhaze wrote (some parts bolded for emphasis):

Would this actually work in real life as real armor? Probably not? But I’m not sure that’s the most important thing to focus on, unless you’re making a gritty, realistic, historically-accurate work. For fantasy? COOLNESS is what counts. I’m all for seeing non-sexualized, diverse ladytypes with functional armor, as long as the coolness factor doesn’t get lost!

In fiction, believability based on realism is much more important than sticking to straight-up realism. As simonjadis says in a reply I reblogged some time ago:

naturalistic story tells a story that is completely plausible in our world. No wizards, no dragons, no secret vampires, no alien invasions. Telling a realistic story is telling a story that is logical and consistent and makes sense (even if the setting is in a fictional world or in a reality very different from our own).

And that’s one of the basic things BABD aims for: promoting female warriors who dress in believable and protective manner, not necessarily realistic/naturalistic.

We criticize bikini armors, boobplates etc. not specifically because they’re historically inaccurate (which they are, but so are dragons and orcs). We criticize them because they’re inconsistent with how most fictional settings work.