Think of it this way.
しょ - The way we say "Oh." Short and sweet
しょう - More like whoa. A little longer
かっこいい - You see the little つ? That makes the next sound (in this case, the K in Ko) a little longer. Kak-koii. It's called a "verbal halt" or something.
びよ - Bee-yo
びょ - Byo
Hope this helped
