Adding images to the .navbar-brand will likely always require custom styles or utilities to properly size. Here are some examples to demonstrate.
So you likely have to play around with the image positioning. Even in their examples they always give the img brand a 30px width and height, it’s probably due to how big is the navbar by default.
My best bet if you want to achieve a custom width/positioning of the image is by wrapping the content of the navbar inside rows and column (grid systems) and work your positioning that way