I was using a mini and didn't realize it until I had my first varsity game. When asking for feedback, my partner told me I needed to be louder and more authoritative on my whistle. I checked, and sure enough, had a mini. Ordered some classics from honigs when I got my new pants, and won't go back to a mini regardless of the gym size (personal preference).
I worked with that partner again last weekend in a middle school tournament, and after the game was over, before I left, he stopped me and mentioned that my whistle sounded louder.
I think the difference is subtle, but other refs will notice and you may seem more unsure of your calls with a softer whistle.