I found something interesting.
With throwdowns in Arcade mode, you get a mixture of blue and red prompts. Blue means you're on 1P side, and that may or may not complete (The term "blue balls" is appropriate here.)
Red means you're on 2P side, and the game starts immediately. (It also means if you have music set to "character" you're always listening to your theme...)
In practice mode, all prompts are red, meaning you are always on 2P side and the game always starts immediately.
This is one tip I'm afraid to share 'cause I might jinx it or something ._.
Don't tell anyone...
ed. wait, I just got a blue. Maybe I just got really lucky... Though, the game did start immediately again.
ed2. ok, I just got denied with a blue again. I suppose it was just a fluke.
A fluke for like... 4 matches in a row... but a fluke nonetheless...
According to the software manual, blue means "challenge accepted by opponent", and red means "challenge received". Well that doesn't explain too much, huh...