It's kinda complicated, but yes, Physique is ultimately the most important stat. There's a target number, which starts at 75 and is modified depending on your stats:
- Height: +5 if you're below 8'6", -5 if you're above 9'
- Willpower quotient, Reflexes quotient and Tone: each of the three give -5 if you have at least 75%, or +5 if you have no more than 25%
- If your milk fullness is at least 90% and your Reflexes quotient is 50% or less, +5
So your final target number will be somewhere between 55 in the best case, and 100 in the worst. This number is then subtracted from your Physique quotient, and that difference determines the result:
- If it's -10 or less, you automatically lose.
- If it's 25 or higher, you win.
- Otherwise, the game adds a random number between 0 and 24; if that brings it above 0, you win.
As such, so long as your Physique beats the target number, you're guaranteed to win, but you've still got a decent chance at up to 9 percentage points lower than the target number: 96% at being exactly equal, -4% for each point below, to a minimum of 60% at -9; anything lower is a guaranteed loss.
Of course, even if you win, you can still decide to throw the match.