I’m using contionuos mode and 175% scale by default. When you’re trying to read a book with pages of various sizes you need to use scroll bar to centralize page by hand. So, there might be advanced setting to centralize page on opening by default, because it’s kinda bothering to drag the scroll bar every time you open a book of this type. And important detail for this hipothetical setting. When you change the scale it changes relative to pointer position, so with this kind of setting, it will cause to displace page from centralized position. So, with this setting page should stay centralized after changing the scale (so you don’t need to mind pointer position).
In conclusion, without this kind of setting, when you open this type of file, you need to drag the scrollbar to see page fully (initial position of scroller is the beggining of scrollbar, so in some cases, when there are really relatively big pages, you don’t see the first page at all), then change scale and centralize page by hand. But with this setting to end up with the same result you just need to change the scale.