No, Fill doesn't mean you get your preferred

If you picked Top/Fill, and you get support, as you're likely to 95% of the time you pick Fill in either secondary or primary, that's your mistake.

If you want top, put top/mid. Mid is the most popular role, so you're least likely to get it instead of your primary.

Basically, if you want any role but mid, put mid as your secondary.

But if you want anything but support, do not put Support or Fill in either slot.